Merge pull request #15823 from yuki24/better-docmentation-for-dynamic-error-pages

ErrorsController shouldn't inherit ApplicationController, but ActionController

guides/source/action_controller_overview.md

@@ -1191,7 +1191,7 @@ Create the controller and views.
 * `app/controllers/errors_controller.rb`
 
   ```ruby
-  class ErrorsController < ApplicationController
+  class ErrorsController < ActionController::Base
     layout 'error'
 
     def not_found