fixing build failure

Author: weaverryan

cookbook/event_dispatcher/event_listener.rst

@@ -223,7 +223,7 @@ Request Events, Checking Types
 A single page can make several requests (one master request, and then multiple
 sub-requests - typically by :ref:`templating-embedding-controller`). For the core
 Symfony events, you might need to check to see if the event is for a "master" request
-or a "sub request":
+or a "sub request"::
 
     // src/AppBundle/EventListener/RequestListener.php
     namespace AppBundle\EventListener;