【Rails】【エラー】undefined method `hosts'

お世話になっております。
Cloud9の環境でrailsを使用してアプリを作成している際にエラーが発生いたしました。
rails db:migrate を行うと下記のエラーが出力されます。

原因がわかる方がいらっしゃいましたらご教授お願いします。

###発生しているエラー

$ rails db:migrate:reset
rails aborted!
NoMethodError: undefined method `hosts' for #<Rails::Application::Configuration:0x0000000002d3a5e8>
/home/ec2-user/.rvm/gems/ruby-2.6.3/gems/railties-5.1.6/lib/rails/railtie/configuration.rb:95:in `method_missing'
/home/ec2-user/environment/coffee_app/config/environments/development.rb:70:in `block in <top (required)>'
・
・
・

該当のソースコード

###config/environments/development.rb

Rails.application.configure do

  config.cache_classes = false

  # Do not eager load code on boot.
  config.eager_load = false

  # Show full error reports.
  config.consider_all_requests_local = true

  # Enable/disable caching. By default caching is disabled.
  # Run rails dev:cache to toggle caching.
  if Rails.root.join('tmp', 'caching-dev.txt').exist?
    config.action_controller.perform_caching = true
    config.action_controller.enable_fragment_cache_logging = true

    config.cache_store = :memory_store
    config.public_file_server.headers = {
      'Cache-Control' => "public, max-age=#{2.days.to_i}"
    }
  else
    config.action_controller.perform_caching = false

    config.cache_store = :null_store
  end

  # Store uploaded files on the local file system (see config/storage.yml for options).
#  config.active_storage.service = :local

  # Don't care if the mailer can't send.
  config.action_mailer.raise_delivery_errors = false

  host = 'rails-tutorial-mhartl.c9users.io' 

  config.action_mailer.default_url_options = { host: host, protocol: 'https' }

  # config.action_mailer.default_url_options = { host: host, protocol: 'http' }

  config.action_mailer.perform_caching = false

  # Print deprecation notices to the Rails logger.
  config.active_support.deprecation = :log

  # Raise an error on page load if there are pending migrations.
  config.active_record.migration_error = :page_load

  # Highlight code that triggered database queries in logs.
  config.active_record.verbose_query_logs = true

  # Debug mode disables concatenation and preprocessing of assets.
  # This option may cause significant delays in view rendering with a large
  # number of complex assets.
  config.assets.debug = true

  # Suppress logger output for asset requests.
  config.assets.quiet = true

  # Raises error for missing translations.
  # config.action_view.raise_on_missing_translations = true

  # Use an evented file watcher to asynchronously detect changes in source code,
  # routes, locales, etc. This feature depends on the listen gem.
  config.file_watcher = ActiveSupport::EventedFileUpdateChecker


  config.hosts.clear
end

###config/environments/production.rb

Rails.application.configure do
  config.cache_classes = true

  config.eager_load = true

  # Full error reports are disabled and caching is turned on.
  config.consider_all_requests_local       = false
  config.action_controller.perform_caching = true

  # Ensures that a master key has been made available in either ENV["RAILS_MASTER_KEY"]
  # or in config/master.key. This key is used to decrypt credentials (and other encrypted files).
  # config.require_master_key = true

  # Disable serving static files from the `/public` folder by default since
  # Apache or NGINX already handles this.
  config.public_file_server.enabled = ENV['RAILS_SERVE_STATIC_FILES'].present?

  # Compress CSS using a preprocessor.
  # config.assets.css_compressor = :sass

  # Do not fallback to assets pipeline if a precompiled asset is missed.
  config.assets.compile = false

  # Enable serving of images, stylesheets, and JavaScripts from an asset server.
  # config.action_controller.asset_host = 'http://assets.example.com'

  # Specifies the header that your server uses for sending files.
  # config.action_dispatch.x_sendfile_header = 'X-Sendfile' # for Apache
  # config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX

  # Store uploaded files on the local file system (see config/storage.yml for options).
#  config.active_storage.service = :local

  # Mount Action Cable outside main process or domain.
  # config.action_cable.mount_path = nil
  # config.action_cable.url = 'wss://example.com/cable'
  # config.action_cable.allowed_request_origins = [ 'http://example.com', /http://example.*/ ]

  # Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
  config.force_ssl = true

  # Use the lowest log level to ensure availability of diagnostic information
  # when problems arise.
  config.log_level = :debug

  # Prepend all log lines with the following tags.
  config.log_tags = [ :request_id ]

  # Use a different cache store in production.
  # config.cache_store = :mem_cache_store

  # Use a real queuing backend for Active Job (and separate queues per environment).
  # config.active_job.queue_adapter     = :resque
  # config.active_job.queue_name_prefix = "sample_app_production"

  config.action_mailer.perform_caching = false

  # Ignore bad email addresses and do not raise email delivery errors.
  # Set this to true and configure the email server for immediate delivery to raise delivery errors.
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.delivery_method = :smtp
  host = '<your heroku app>.herokuapp.com'
  config.action_mailer.default_url_options = { host: host }
  ActionMailer::Base.smtp_settings = {
    :address        => 'smtp.sendgrid.net',
    :port           => '587',
    :authentication => :plain,
    :user_name      => ENV['SENDGRID_USERNAME'],
    :password       => ENV['SENDGRID_PASSWORD'],
    :domain         => 'heroku.com',
    :enable_starttls_auto => true
  }

  # Enable locale fallbacks for I18n (makes lookups for any locale fall back to
  # the I18n.default_locale when a translation cannot be found).
  config.i18n.fallbacks = true

  # Send deprecation notices to registered listeners.
  config.active_support.deprecation = :notify

  # Use default logging formatter so that PID and timestamp are not suppressed.
  config.log_formatter = ::Logger::Formatter.new

  # Use a different logger for distributed setups.
  # require 'syslog/logger'
  # config.logger = ActiveSupport::TaggedLogging.new(Syslog::Logger.new 'app-name')

  if ENV["RAILS_LOG_TO_STDOUT"].present?
    logger           = ActiveSupport::Logger.new(STDOUT)
    logger.formatter = config.log_formatter
    config.logger    = ActiveSupport::TaggedLogging.new(logger)
  end

  # Do not dump schema after migrations.
  config.active_record.dump_schema_after_migration = false

  # Inserts middleware to perform automatic connection switching.
  # The `database_selector` hash is used to pass options to the DatabaseSelector
  # middleware. The `delay` is used to determine how long to wait after a write
  # to send a subsequent read to the primary.
  #
  # The `database_resolver` class is used by the middleware to determine which
  # database is appropriate to use based on the time delay.
  #
  # The `database_resolver_context` class is used by the middleware to set
  # timestamps for the last write to the primary. The resolver uses the context
  # class timestamps to determine how long to wait before reading from the
  # replica.
  #
  # By default Rails will store a last write timestamp in the session. The
  # DatabaseSelector middleware is designed as such you can define your own
  # strategy for connection switching and pass that into the middleware through
  # these configuration options.
  # config.active_record.database_selector = { delay: 2.seconds }
  # config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
  # config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
end

###config/environments/test.rb

Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  config.cache_classes = false

  # Do not eager load code on boot. This avoids loading your whole application
  # just for the purpose of running a single test. If you are using a tool that
  # preloads Rails for running tests, you may have to set it to true.
  config.eager_load = false

  # Configure public file server for tests with Cache-Control for performance.
  config.public_file_server.enabled = true
  config.public_file_server.headers = {
    'Cache-Control' => "public, max-age=#{1.hour.to_i}"
  }

  # Show full error reports and disable caching.
  config.consider_all_requests_local       = true
  config.action_controller.perform_caching = false
  config.cache_store = :null_store

  # Raise exceptions instead of rendering exception templates.
  config.action_dispatch.show_exceptions = false

  # Disable request forgery protection in test environment.
  config.action_controller.allow_forgery_protection = false

  # Store uploaded files on the local file system in a temporary directory.
#  config.active_storage.service = :test

  config.action_mailer.perform_caching = false

  # Tell Action Mailer not to deliver emails to the real world.
  # The :test delivery method accumulates sent emails in the
  # ActionMailer::Base.deliveries array.
  config.action_mailer.delivery_method = :test
  config.action_mailer.default_url_options = { host: 'localhost:3000' }

  # Print deprecation notices to the stderr.
  config.active_support.deprecation = :stderr

  # Raises error for missing translations.
  # config.action_view.raise_on_missing_translations = true
end

他にも確認するべきソースコードがございましたらご連絡をお願いいたします。