Fix YAML config bug

Should be merged into all version branches

Author: Holicz

event_dispatcher.rst

@@ -77,7 +77,8 @@ using a special "tag":
 
         # app/config/services.yml
         services:
-            AppBundle\EventListener\ExceptionListener:
+            app.exception_listener:
+                class: AppBundle\EventListener\ExceptionListener:
                 tags:
                     - { name: kernel.event_listener, event: kernel.exception }