[ci skip] Update rails/all.rb reference.

It didn't mention Action Cable's engine.

guides/source/initialization.md

@@ -530,16 +530,17 @@ This file is responsible for requiring all the individual frameworks of Rails:
 require "rails"
 
 %w(
-  active_record
-  action_controller
-  action_view
-  action_mailer
-  active_job
-  rails/test_unit
-  sprockets
-).each do |framework|
+  active_record/railtie
+  action_controller/railtie
+  action_view/railtie
+  action_mailer/railtie
+  active_job/railtie
+  action_cable/engine
+  rails/test_unit/railtie
+  sprockets/railtie
+).each do |railtie|
   begin
-    require "#{framework}/railtie"
+    require "#{railtie}"
   rescue LoadError
   end
 end