add serializer to activityController

src/Bundle/ChillActivityBundle/config/services/controller.yaml

@@ -4,4 +4,5 @@ services:
             $eventDispatcher: '@Symfony\Component\EventDispatcher\EventDispatcherInterface'
             $authorizationHelper: '@Chill\MainBundle\Security\Authorization\AuthorizationHelper'
             $logger: '@chill.main.logger'
+            $serializer: '@Symfony\Component\Serializer\SerializerInterface'
         tags: ['controller.service_arguments']