Fix missing "-" in salt-key help text, "-L" line.

I'm pretty sure it's supposed to read `(Deprecated: use "--list-all")` since there's no `salt-key --list all` command.

```
root@salt:~# salt-key -h
Usage: salt-key [options]

Salt key is used to manage Salt authentication keys
...
    -L, --list-all      List all public keys. (Deprecated: use "--list all")
...
```