Rails　uninitialized constant Rack::Cors (NameError) の解消

前提・実現したいこと

RailsAPIでオリジンからのアクセスを許可し、フロントエンドからAPIを叩きたいです。
その際、
gem rack-corsの追加
bundleの実行
cors.rbの編集（以下参照）
を行いました。

ruby
1#cors.rb
2# Be sure to restart your server when you modify this file.
3
4# Avoid CORS issues when API is called from the frontend app.
5# Handle Cross-Origin Resource Sharing (CORS) in order to accept cross-origin AJAX requests.
6
7# Read more: https://github.com/cyu/rack-cors
8
9Rails.application.config.middleware.insert_before 0, Rack::Cors do
10	allow do
11		origins '*'
12		resource '*',
13		headers: :any,
14		methods: [:get, :post, :put, :patch, :delete, :options, :head]
15	end
16end
17

発生している問題・エラーメッセージ

NameErrorが発生してしまいます

api_1    | /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:80:in `block in load_missing_constant': uninitialized constant Rack::Cors (NameError)
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:9:in `without_bootsnap_cache'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:80:in `rescue in load_missing_constant'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:59:in `load_missing_constant'
api_1    |      from /app_name/api/config/application.rb:25:in `<class:Application>'
api_1    |      from /app_name/api/config/application.rb:21:in `<module:Api>'
api_1    |      from /app_name/api/config/application.rb:20:in `<top (required)>'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/commands/server/server_command.rb:145:in `block in perform'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/commands/server/server_command.rb:142:in `tap'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/commands/server/server_command.rb:142:in `perform'
api_1    |      from /usr/local/bundle/gems/thor-1.0.1/lib/thor/command.rb:27:in `run'
api_1    |      from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:127:in `invoke_command'
api_1    |      from /usr/local/bundle/gems/thor-1.0.1/lib/thor.rb:392:in `dispatch'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/command/base.rb:69:in `perform'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/command.rb:46:in `invoke'
api_1    |      from /usr/local/bundle/gems/railties-5.2.4.3/lib/rails/commands.rb:18:in `<top (required)>'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
api_1    |      from /usr/local/bundle/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
api_1    |      from bin/rails:4:in `<main>'
prologue_api_1 exited with code 1