copy files on macOS X return error: "could not copy extended attributes"

When I try to copy file to a `utahfs-client` mounted folder on macOS X with latest version `utahfs-client` binary, and the command `cp` returns with error:

```
# cp **** .
cp: ****: could not copy extended attributes to ./****: Operation not permitted
```

while `utahfs-client` printed following logs:

```
# utahfs-client -cfg ~/.utahfs/utahfs.yaml -mount ~/utahfs
Password:
2020/06/28 15:01:52 main.go:73: filesystem successfully mounted
fuse: 2020/06/28 15:01:52 connection.go:499: *fuseops.GetXattrOp error: function not implemented
fuse: 2020/06/28 15:02:00 connection.go:499: *fuseops.ListXattrOp error: function not implemented
fuse: 2020/06/28 15:02:49 connection.go:499: *fuseops.SetXattrOp error: function not implemented
```