stat: should fail without arguments

When running `stat` without arguments, GNU `stats` fails:
```
$ /usr/bin/stat
/usr/bin/stat: missing operand
Try '/usr/bin/stat --help' for more information.
$ echo $?
1
```
uutils `stat`, on the other hand, doesn't output anything and doesn't fail:
```
$ cargo run --features=unix stat
$ echo $?
0
```