Get python too

Lower the barrier to entry to get someone to write support for [fabric](http://www.fabfile.org/).

```
Running `bash` attached to terminal... up, run.9358
~ $ which cap
/app/bin/cap
~ $ which fab
/app/.heroku/python/bin/fab
~ $ fab --version
Fabric 1.8.3
Paramiko 1.12.4
~ $ cap --version
Capistrano v2.9.0
~ $ exit
```