Fix the detection of the deprecated usage of the ValidationListener

Author: stof

Extension/Validator/EventListener/ValidationListener.php

@@ -46,7 +46,7 @@ public function __construct($validator, ViolationMapperInterface $violationMappe
             throw new \InvalidArgumentException('Validator must be instance of Symfony\Component\Validator\Validator\ValidatorInterface or Symfony\Component\Validator\ValidatorInterface');
         }
 
-        if ($validator instanceof LegacyValidatorInterface) {
+        if (!$validator instanceof ValidatorInterface) {
             @trigger_error('Passing an instance of Symfony\Component\Validator\ValidatorInterface as argument to the '.__METHOD__.' method is deprecated since version 2.8 and will be removed in 3.0. Use an implementation of Symfony\Component\Validator\Validator\ValidatorInterface instead', E_USER_DEPRECATED);
         }