corrected the location of status code symbols

actionpack/lib/action_dispatch/testing/assertions/response.rb

@@ -20,7 +20,7 @@ module ResponseAssertions
       #
       # You can also pass an explicit status number like <tt>assert_response(501)</tt>
       # or its symbolic equivalent <tt>assert_response(:not_implemented)</tt>.
-      # See ActionDispatch::StatusCodes for a full list.
+      # See Rack::Utils::SYMBOL_TO_STATUS_CODE for a full list.
       #
       # ==== Examples
       #