[Serializer] Improve a deprecation message

Author: GuilhemN

Mapping/Factory/ClassMetadataFactory.php

@@ -50,7 +50,7 @@ public function __construct(LoaderInterface $loader, Cache $cache = null)
         $this->cache = $cache;
 
         if (null !== $cache) {
-            @trigger_error(sprintf('Passing a Doctrine Cache instance as 2nd parameter of the "%s" constructor is deprecated. This parameter will be removed in Symfony 4.0. Use the "%s" class instead.', __CLASS__, CacheClassMetadataFactory::class), E_USER_DEPRECATED);
+            @trigger_error(sprintf('Passing a Doctrine Cache instance as 2nd parameter of the "%s" constructor is deprecated since version 3.1. This parameter will be removed in Symfony 4.0. Use the "%s" class instead.', __CLASS__, CacheClassMetadataFactory::class), E_USER_DEPRECATED);
         }
     }