站内信列表返回创建时间

app/Http/Resources/API/NotificationCollection.php

@@ -43,6 +43,7 @@ class NotificationCollection extends ResourceCollection
             $row = [
                 'id' => $item->id,
                 'object_type' => $item->object_type,
+                'created_at'=>(string)$item->created_at,
                 'content' => $item->content,
                 'read_at' => (string)$item->read_at,
                 'read_status' => (bool)$item->read_at,