Use escaped backslashes

Author: adursun

routing.rst

@@ -689,7 +689,7 @@ Troubleshooting
 
 Here are some common errors you might see while working with routing:
 
-    Controller "AppBundle\Controller\BlogController::showAction()" requires that you
+    Controller "AppBundle\\Controller\\BlogController::showAction()" requires that you
     provide a value for the "$slug" argument.
 
 This happens when your controller method has an argument (e.g. ``$slug``)::