No commands appear to work for choosenim on OSX
Trying to use a fresh choosenim install on OSX doesn't appear to work:
```
$ choosenim #head
choosenim: The Nim toolchain installer.

Usage:
  choosenim <version/path/channel>

[...]
```

```
$ choosenim update #head
       Tip: 4 messages have been suppressed, use --verbose to show them.
     Error: choosenim.nim(206)       choosenim
        ... choosenim.nim(183)       performAction
        ... choosenim.nim(127)       update
        ... Expected 1 parameter to 'update' command
```

I've tried a number of other commands, all of which have messages similar or same as the ones above.