Herokuへデプロイできない。Rails Tutorial

Rails Tutorialで勉強中に第２章のHerokuへデプロイするときにエラーが発生しました。Applivcation Errorと出て、ページが表示されません。

発生している問題・エラーメッセージ

エラーメッセージ
Application error
An error occurred in the application and your page could not be served.

Heroku logs の結果が以下です。


2018-07-28T02:38:03.616238+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
2018-07-28T02:38:03.616239+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/railties-5.1.6/lib/rails/rack/logger.rb:36:in `call_app'
2018-07-28T02:38:03.616240+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/railties-5.1.6/lib/rails/rack/logger.rb:24:in `block in call'
2018-07-28T02:38:03.616242+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/tagged_logging.rb:69:in `block in tagged'
2018-07-28T02:38:03.616243+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/tagged_logging.rb:26:in `tagged'
2018-07-28T02:38:03.616244+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/tagged_logging.rb:69:in `tagged'
2018-07-28T02:38:03.616245+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/railties-5.1.6/lib/rails/rack/logger.rb:24:in `call'
2018-07-28T02:38:03.616246+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
2018-07-28T02:38:03.616247+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_dispatch/middleware/request_id.rb:25:in `call'
2018-07-28T02:38:03.616252+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/rack-2.0.5/lib/rack/method_override.rb:22:in `call'
2018-07-28T02:38:03.616253+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/rack-2.0.5/lib/rack/runtime.rb:22:in `call'
2018-07-28T02:38:03.616256+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/activesupport-5.1.6/lib/active_support/cache/strategy/local_cache_middleware.rb:27:in `call'
2018-07-28T02:38:03.616257+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_dispatch/middleware/executor.rb:12:in `call'
2018-07-28T02:38:03.616258+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/actionpack-5.1.6/lib/action_dispatch/middleware/static.rb:125:in `call'
2018-07-28T02:38:03.616259+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/rack-2.0.5/lib/rack/sendfile.rb:111:in `call'
2018-07-28T02:38:03.616260+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/railties-5.1.6/lib/rails/engine.rb:522:in `call'
2018-07-28T02:38:03.616261+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/puma-3.9.1/lib/puma/configuration.rb:224:in `call'
2018-07-28T02:38:03.616262+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/puma-3.9.1/lib/puma/server.rb:602:in `handle_request'
2018-07-28T02:38:03.616263+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/puma-3.9.1/lib/puma/server.rb:435:in `process_client'
2018-07-28T02:38:03.616264+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/puma-3.9.1/lib/puma/server.rb:299:in `block in run'
2018-07-28T02:38:03.616265+00:00 app[web.1]: [25648681-ba25-4f7f-bf5a-ba29e1c621e8] vendor/bundle/ruby/2.4.0/gems/puma-3.9.1/lib/puma/thread_pool.rb:120:in `block in spawn_thread'
2018-07-28T02:38:04.251718+00:00 heroku[router]: at=info method=GET path="/favicon.ico" host=protected-peak-92868.herokuapp.com request_id=13c7a17c-fa65-464f-ad7f-c9c8229d5e6a fwd="111.239.163.247" dyno=web.1 connect=1ms service=2ms status=304 bytes=48 protocol=https
2018-07-28T02:52:21.000000+00:00 app[api]: Build started by user mgr31029@gmail.com
2018-07-28T02:52:41.303841+00:00 app[api]: Deploy 645400d4 by user mgr31029@gmail.com
2018-07-28T02:52:41.303841+00:00 app[api]: Release v6 created by user mgr31029@gmail.com
2018-07-28T02:52:41.564125+00:00 heroku[web.1]: Restarting
2018-07-28T02:52:41.565576+00:00 heroku[web.1]: State changed from up to starting
2018-07-28T02:52:42.256132+00:00 app[web.1]: - Gracefully stopping, waiting for requests to finish
2018-07-28T02:52:42.256252+00:00 app[web.1]: === puma shutdown: 2018-07-28 02:52:42 +0000 ===
2018-07-28T02:52:42.256259+00:00 app[web.1]: - Goodbye!
2018-07-28T02:52:42.256297+00:00 app[web.1]: Exiting
2018-07-28T02:52:42.245443+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2018-07-28T02:52:42.318481+00:00 heroku[web.1]: Process exited with status 0
2018-07-28T02:52:44.125221+00:00 heroku[web.1]: Starting process with command `bin/rails server -p 28508 -e production`
2018-07-28T02:52:44.000000+00:00 app[api]: Build succeeded
2018-07-28T02:52:48.561637+00:00 app[web.1]: => Booting Puma
2018-07-28T02:52:48.561655+00:00 app[web.1]: => Rails 5.1.6 application starting in production
2018-07-28T02:52:48.561657+00:00 app[web.1]: => Run `rails server -h` for more startup options
2018-07-28T02:52:48.561659+00:00 app[web.1]: Puma starting in single mode...
2018-07-28T02:52:48.561665+00:00 app[web.1]: * Version 3.9.1 (ruby 2.4.4-p296), codename: Private Caller
2018-07-28T02:52:48.561667+00:00 app[web.1]: * Min threads: 5, max threads: 5
2018-07-28T02:52:48.561669+00:00 app[web.1]: * Environment: production
2018-07-28T02:52:48.561802+00:00 app[web.1]: * Listening on tcp://0.0.0.0:28508
2018-07-28T02:52:48.562248+00:00 app[web.1]: Use Ctrl-C to stop
2018-07-28T02:52:48.946328+00:00 heroku[web.1]: State changed from starting to up

検索したのですがエラーの原因がわからないため、ご教授よろしくお願いしますm()m