Incorrectly categorises pre-release version of Python as "stable"

```
$ p ls stable
```

Incorrectly gives me 

```
3.6.0
```

https://www.python.org/downloads/ shows 3.5.2 as the latest release.

https://www.python.org/download/pre-releases/ shows 3.6.0a3 as the current pre-release testing version.
