[softdeleteable] avoid validation error on mapped superclass. fix #490

lib/Gedmo/SoftDeleteable/Mapping/Validator.php

@@ -34,6 +34,10 @@ class Validator
 
     public static function validateField(ClassMetadataInfo $meta, $field)
     {
+        if ($meta->isMappedSuperclass) {
+            return;
+        }
+
         $fieldMapping = $meta->getFieldMapping($field);
 
         if (!in_array($fieldMapping['type'], self::$validTypes)) {