前提・実現したいこと

現在、Railsチュートリアルの２章を進めている初心者です。
２章の序盤にて、git heroku push masterを行うのですが、下記のようなエラーが出てしまいました。
１章のgit heroku push masterが同じ手順で成功したため、２章のエラーが何なのかがわからない状態です。

発生している問題・エラーメッセージ

膨大なpush実行文のうち、以下の部分が原因だろうか？と個人的に考えていました。

-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.5.5
-----> Installing dependencies using bundler 2.0.2
       Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
       The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
〜略〜
remote:  !
remote:  !     Could not detect rake tasks
remote:  !     ensure you can run `$ bundle exec rake -P` against your app
remote:  !     and using the production group of your Gemfile.
remote:  !     Activating bundler (2.0.1) failed:
remote:  !     Could not find 'bundler' (2.0.1) required by your /tmp/build_ecaa2911b7de7674a34f8dd4c80f6e39/Gemfile.lock.
remote:  !     To update to the latest version installed on your system, run `bundle update --bundler`.
remote:  !     To install the missing version, run `gem install bundler:2.0.1`
remote:  !     Checked in 'GEM_PATH=vendor/bundle/ruby/2.5.0', execute `gem env` for more information
remote:  !     
remote:  !     To install the version of bundler this project requires, run `gem install bundler -v '2.0.1'`
remote:  !
〜略〜
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/mysterious-inlet-51368.git'

試したこと

まず最初の-----> Ruby app detected　以下にある、

$ bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java

を試してみるもののエラーは変わらず、
Could not detect rake tasks以下に記載されている通りに、

$ bundle exec rake -P
$ bundle update --bundler
$ gem install bundler:2.0.1
$ gem install bundler -v '2.0.1'

などのコマンドを試してからpushしても、同じエラー文が出てくるだけでした。
ただ、 'GEM_PATH=vendor/bundle/ruby/2.5.0'という部分を、$ gem envで確認したところ、

RubyGems Environment:
  - RUBYGEMS VERSION: 2.7.6
  - RUBY VERSION: 2.5.3 (2018-10-18 patchlevel 105) [x86_64-darwin18]
  - INSTALLATION DIRECTORY: /Users/~/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0
  - USER INSTALLATION DIRECTORY: /Users/~/.gem/ruby/2.5.0
  - RUBY EXECUTABLE: /Users/~/.rbenv/versions/2.5.3/bin/ruby
  - EXECUTABLE DIRECTORY: /Users/~/.rbenv/versions/2.5.3/bin
  - SPEC CACHE DIRECTORY: /Users/~/.gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: /Users/~/.rbenv/versions/2.5.3/etc
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-18
  - GEM PATHS:
     - /Users/~/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0
     - /Users/~/.gem/ruby/2.5.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - /Users/~/.rbenv/versions/2.5.3/bin
     - /usr/local/Cellar/rbenv/1.1.1/libexec
     - /Users/~/.nodebrew/current/bin
     - /Users/~/.rbenv/shims
     - /Users/~/.rbenv/shims
     - /Users/~/.pyenv/shims
     - /usr/local/bin
     - /usr/bin
     - /bin
     - /usr/sbin
     - /sbin

'GEM_PATH=vendor/bundle/ruby/2.5.0'と同じよう記述がないのが気になっています。
しかし、検索をかけても何をすれば良いかヒットしないため、お手上げ状態です。

補足情報（FW/ツールのバージョンなど）

参考までにGemfileとGemfile.lockを記載いたします。
#Gemfile

source 'https://rubygems.org'

git_source(:github) do |repo_name|
  repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
  "https://github.com/#{repo_name}.git"
end

gem 'rails', '5.1.6'
gem 'puma', '3.9.1'
gem 'sass-rails', '5.0.6'
gem 'uglifier', '3.2.0'
gem 'coffee-rails', '4.2.2'
gem 'jquery-rails', '4.3.1'
gem 'turbolinks', '5.0.1'
gem 'jbuilder', '2.7.0'

group :development, :test do
  gem 'sqlite3', '1.3.13'
  gem 'byebug', '9.0.6', platforms: :mri
  gem 'capybara', '2.13'
  gem 'selenium-webdriver'
end

group :development do
  gem 'web-console', '3.5.1'
  gem 'listen', '3.1.5'
  gem 'spring', '2.0.2'
  gem 'spring-watcher-listen', '2.0.1'
end

group :production do
  gem 'pg', '0.20.0'
end

gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    actioncable (5.1.6)
      actionpack (= 5.1.6)
      nio4r (~> 2.0)
      websocket-driver (~> 0.6.1)
    actionmailer (5.1.6)
      actionpack (= 5.1.6)
      actionview (= 5.1.6)
      activejob (= 5.1.6)
      mail (~> 2.5, >= 2.5.4)
      rails-dom-testing (~> 2.0)
    actionpack (5.1.6)
      actionview (= 5.1.6)
      activesupport (= 5.1.6)
      rack (~> 2.0)
      rack-test (>= 0.6.3)
      rails-dom-testing (~> 2.0)
      rails-html-sanitizer (~> 1.0, >= 1.0.2)
    actionview (5.1.6)
      activesupport (= 5.1.6)
      builder (~> 3.1)
      erubi (~> 1.4)
      rails-dom-testing (~> 2.0)
      rails-html-sanitizer (~> 1.0, >= 1.0.3)
    activejob (5.1.6)
      activesupport (= 5.1.6)
      globalid (>= 0.3.6)
    activemodel (5.1.6)
      activesupport (= 5.1.6)
    activerecord (5.1.6)
      activemodel (= 5.1.6)
      activesupport (= 5.1.6)
      arel (~> 8.0)
    activesupport (5.1.6)
      concurrent-ruby (~> 1.0, >= 1.0.2)
      i18n (>= 0.7, < 2)
      minitest (~> 5.1)
      tzinfo (~> 1.1)
    addressable (2.6.0)
      public_suffix (>= 2.0.2, < 4.0)
    arel (8.0.0)
    bindex (0.7.0)
    builder (3.2.3)
    byebug (9.0.6)
    capybara (2.13.0)
      addressable
      mime-types (>= 1.16)
      nokogiri (>= 1.3.3)
      rack (>= 1.0.0)
      rack-test (>= 0.5.4)
      xpath (~> 2.0)
    childprocess (1.0.1)
      rake (< 13.0)
    coffee-rails (4.2.2)
      coffee-script (>= 2.2.0)
      railties (>= 4.0.0)
    coffee-script (2.4.1)
      coffee-script-source
      execjs
    coffee-script-source (1.12.2)
    concurrent-ruby (1.1.5)
    crass (1.0.4)
    erubi (1.8.0)
    execjs (2.7.0)
    ffi (1.11.1)
    globalid (0.4.2)
      activesupport (>= 4.2.0)
    i18n (1.6.0)
      concurrent-ruby (~> 1.0)
    jbuilder (2.7.0)
      activesupport (>= 4.2.0)
      multi_json (>= 1.2)
    jquery-rails (4.3.1)
      rails-dom-testing (>= 1, < 3)
      railties (>= 4.2.0)
      thor (>= 0.14, < 2.0)
    listen (3.1.5)
      rb-fsevent (~> 0.9, >= 0.9.4)
      rb-inotify (~> 0.9, >= 0.9.7)
      ruby_dep (~> 1.2)
    loofah (2.2.3)
      crass (~> 1.0.2)
      nokogiri (>= 1.5.9)
    mail (2.7.1)
      mini_mime (>= 0.1.1)
    method_source (0.9.2)
    mime-types (3.2.2)
      mime-types-data (~> 3.2015)
    mime-types-data (3.2019.0331)
    mini_mime (1.0.1)
    mini_portile2 (2.4.0)
    minitest (5.11.3)
    multi_json (1.13.1)
    nio4r (2.3.1)
    nokogiri (1.10.3)
      mini_portile2 (~> 2.4.0)
    pg (0.20.0)
    public_suffix (3.1.1)
    puma (3.9.1)
    rack (2.0.7)
    rack-test (1.1.0)
      rack (>= 1.0, < 3)
    rails (5.1.6)
      actioncable (= 5.1.6)
      actionmailer (= 5.1.6)
      actionpack (= 5.1.6)
      actionview (= 5.1.6)
      activejob (= 5.1.6)
      activemodel (= 5.1.6)
      activerecord (= 5.1.6)
      activesupport (= 5.1.6)
      bundler (>= 1.3.0)
      railties (= 5.1.6)
      sprockets-rails (>= 2.0.0)
    rails-dom-testing (2.0.3)
      activesupport (>= 4.2.0)
      nokogiri (>= 1.6)
    rails-html-sanitizer (1.0.4)
      loofah (~> 2.2, >= 2.2.2)
    railties (5.1.6)
      actionpack (= 5.1.6)
      activesupport (= 5.1.6)
      method_source
      rake (>= 0.8.7)
      thor (>= 0.18.1, < 2.0)
    rake (12.3.2)
    rb-fsevent (0.10.3)
    rb-inotify (0.10.0)
      ffi (~> 1.0)
    ruby_dep (1.5.0)
    rubyzip (1.2.3)
    sass (3.7.4)
      sass-listen (~> 4.0.0)
    sass-listen (4.0.0)
      rb-fsevent (~> 0.9, >= 0.9.4)
      rb-inotify (~> 0.9, >= 0.9.7)
    sass-rails (5.0.6)
      railties (>= 4.0.0, < 6)
      sass (~> 3.1)
      sprockets (>= 2.8, < 4.0)
      sprockets-rails (>= 2.0, < 4.0)
      tilt (>= 1.1, < 3)
    selenium-webdriver (3.142.3)
      childprocess (>= 0.5, < 2.0)
      rubyzip (~> 1.2, >= 1.2.2)
    spring (2.0.2)
      activesupport (>= 4.2)
    spring-watcher-listen (2.0.1)
      listen (>= 2.7, < 4.0)
      spring (>= 1.2, < 3.0)
    sprockets (3.7.2)
      concurrent-ruby (~> 1.0)
      rack (> 1, < 3)
    sprockets-rails (3.2.1)
      actionpack (>= 4.0)
      activesupport (>= 4.0)
      sprockets (>= 3.0.0)
    sqlite3 (1.3.13)
    thor (0.20.3)
    thread_safe (0.3.6)
    tilt (2.0.9)
    turbolinks (5.0.1)
      turbolinks-source (~> 5)
    turbolinks-source (5.2.0)
    tzinfo (1.2.5)
      thread_safe (~> 0.1)
    uglifier (3.2.0)
      execjs (>= 0.3.0, < 3)
    web-console (3.5.1)
      actionview (>= 5.0)
      activemodel (>= 5.0)
      bindex (>= 0.4.0)
      railties (>= 5.0)
    websocket-driver (0.6.5)
      websocket-extensions (>= 0.1.0)
    websocket-extensions (0.1.4)
    xpath (2.1.0)
      nokogiri (~> 1.3)

PLATFORMS
  ruby

DEPENDENCIES
  byebug (= 9.0.6)
  capybara (= 2.13)
  coffee-rails (= 4.2.2)
  jbuilder (= 2.7.0)
  jquery-rails (= 4.3.1)
  listen (= 3.1.5)
  pg (= 0.20.0)
  puma (= 3.9.1)
  rails (= 5.1.6)
  sass-rails (= 5.0.6)
  selenium-webdriver
  spring (= 2.0.2)
  spring-watcher-listen (= 2.0.1)
  sqlite3 (= 1.3.13)
  turbolinks (= 5.0.1)
  tzinfo-data
  uglifier (= 3.2.0)
  web-console (= 3.5.1)

BUNDLED WITH
   2.0.1

どうぞよろしくお願いします。