date: --universal not working

`--universal`(or `--utc`) doesn't work to set the time zone to UTC
`TZ=Etc/UTC` still works

```
$ uu-date --universal --date @0
Wed Dec 31 19:00:00 1969

$ TZ=Etc/UTC uu-date --date @0
Thu Jan  1 00:00:00 1970

#GNU
$ date --universal --date @0
Thu Jan  1 00:00:00 UTC 1970
```