Add a newline to the output of `arc help --full`.

Summary: The output from `arc help --full` is missing a newline character.

Test Plan:
**Before**
```
> arc help --full
      --skip-arcconfig
           Skip the working copy configuration file

      --arcrc-file filename
           Use provided file instead of ~/.arcrc.>
```

**After**
```
> arc help --full
      --skip-arcconfig
           Skip the working copy configuration file

      --arcrc-file filename
           Use provided file instead of ~/.arcrc.
>
```

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9608