Error on get_drive()$upload_file

When trying to upload a file to a sharepoint directory, an error is reported from `httr::content`. Similar to #221, the file is actually uploaded.

```
sh_site <- get_sharepoint_site()
sh_site$get_drive()$upload_file(local_file, sharepoint_file)
```

Results in
```
Error in httr::content(res) (from xyz.R) : is.response(x) is not TRUE
```

However the file is now in the directory.

Reproduce the issue with get_sharepoint_site() and get_drive()$upload_file(local_file, sharepoint_file), then inspect the upload path around the httr::content(res) call reported from xyz.R. Compare the behavior with issue #221; done means the file is uploaded and the call completes without the is.response error.

Written by the indexing model from the issue text.