Use MongoId::isValid instead of own implementation

Author: jenssegers

src/Jenssegers/Mongodb/Query/Builder.php

@@ -790,7 +790,7 @@ protected function performUpdate($query, array $options = [])
      */
     public function convertKey($id)
     {
-        if (is_string($id) and strlen($id) === 24 and ctype_xdigit($id))
+        if (MongoId::isValid($id))
         {
             return new MongoId($id);
         }