Added the missing "use" import for the Response class

Author: javiereguiluz

security/guard_authentication.rst

@@ -155,6 +155,7 @@ This requires you to implement six methods::
 
     use Symfony\Component\HttpFoundation\Request;
     use Symfony\Component\HttpFoundation\JsonResponse;
+    use Symfony\Component\HttpFoundation\Response;
     use Symfony\Component\Security\Core\User\UserInterface;
     use Symfony\Component\Security\Guard\AbstractGuardAuthenticator;
     use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;