Fix SyncRelated not triggering sync related

Fix SyncRelated not triggering syncRelatedWithFirebase() in parent

Author: plokko

src/Relations/SyncWithFirebaseBelongsToMany.php

@@ -72,6 +72,7 @@ protected function syncParentWithFirebase(){
         if($this->_isSynching){
             //TODO:should only update touched relation
             $this->parent->syncWithFirebase();
+            $this->parent->syncRelatedWithFirebase();
         }
     }
-}
+}