message: wait the task end;
diff: @@ -50,7 +50,7 @@ DownloadService.downloadTask = function (option: DownloadService.Option | string
  context.update(prog, total);
  };
  }
  - defaultDownloadService.download(option, destination as string);
  + return defaultDownloadService.download(option, destination as string);
  };
  } as any;
  