Elide "exercism configure --dir" with no value
Elide "exercism configure --dir" with no value

Running "exercism configure --dir" doesn't appear to work as described.

```bash
$ exercism configure --dir
Incorrect Usage.

NAME:
   exercism configure - Writes config values to a JSON file.

USAGE:
   exercism configure [command options] [arguments...]

OPTIONS:
   --dir value, -d value   path to exercises directory
   --host value, -u value  exercism api host
   --key value, -k value   exercism.io API key (see http://exercism.io/account/key)
   --api value, -a value   exercism xapi host
   
2017/01/14 08:43:05 flag needs an argument: -dir
```

In any case, it was right there in the debug output; why not do the same as the API Key above and just say look at it?
tejasbubane/exercism.io,treiff/exercism.io,treiff/exercism.io,RaptorRCX/exercism.io,treiff/exercism.io,tejasbubane/exercism.io,treiff/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,RaptorRCX/exercism.io