这样初始化一个message： let message = AVIMVideoMessage(text: "", attachedFilePath: path, attributes: [:])，path为手机相册对应视频资源的path，之前还能发送，昨天测试了一下，有些能可以发送，大部分发送失败，错误日志如下：
------ BEGIN LeanCloud REST Response ------
path: /1.1/classes/_file/56de3ecbefa631005ec041fc
cost: 4.831s
response: Error Domain=AVNetworkingErrorDomain Code=-1011 "Expected status code in (200 ~ 203), got 403" UserInfo={NSErrorFailingURLKey=https://api.leancloud.cn/1.1/classes/_file/56de3ecbefa631005ec041fc, NSLocalizedDescription=Expected status code in (200 ~ 203), got 403, NSLocalizedRecoverySuggestion={"code":1,"error":"Forbidden to delete by class permissions."}}
------ END --------------------------------
2016-03-08 10:54:08.801 AiGolf[14758:6654891] [ERROR] +[AVErrorUtils errorFromJSON:] [Line 197] error: Error Domain=AVOS Cloud Error Domain Code=1 "Forbidden to delete by class permissions." UserInfo={error=Forbidden to delete by class permissions., NSLocalizedDescription=Forbidden to delete by class permissions., code=1}