visionmedia/n — pull request #137 by jeromedecoster (2013-07-09 16:23:19+00:00)
Title: abort gracefully if no installed version

When you use n for the first time or if you have removed all the versions under `/usr/local/n/versions` it shows a strange empty message:

```bash

*

```

This fix just check if there is at least one directory inside `$VERSIONS_DIR`
If no, abort gracefully with the error:

```bash
$ n

Error: no installed version

```