Small code tweaks

Author: abluchet

src/EventListener/WriteListener.php

@@ -22,7 +22,7 @@
  * @author Kévin Dunglas <[email protected]>
  * @author Baptiste Meyer <[email protected]>
  */
-class WriteListener
+final class WriteListener
 {
     private $dataPersister;
 

src/HttpCache/EventListener/AddTagsListener.php

@@ -66,6 +66,6 @@ public function onKernelResponse(FilterResponseEvent $event)
             return;
         }
 
-        $event->getResponse()->headers->set('Cache-Tags', implode(',', $resources));
+        $response->headers->set('Cache-Tags', implode(',', $resources));
     }
 }