use `ActiveSupport::Reloader.to_prepare` instead of deprecated...

use `ActiveSupport::Reloader.to_prepare` instead of deprecated `ActionDispatch::Reloader.to_prepare` [ci skip]

activesupport/lib/active_support/file_update_checker.rb

@@ -23,7 +23,7 @@ module ActiveSupport
   #     I18n.reload!
   #   end
   #
-  #   ActionDispatch::Reloader.to_prepare do
+  #   ActiveSupport::Reloader.to_prepare do
   #     i18n_reloader.execute_if_updated
   #   end
   class FileUpdateChecker