feat(client): optional drink of choice

[ask and ye shall receive](https://botbot.me/freenode/deis/2014-11-05/?msg=24906137&page=4):

```
><> deis apps
=== Apps
><> deis ps:scale web=2
Scaling processes... but first, coffee!
404 NOT FOUND
Detail:
Not found
><> export DEIS_DRINK_OF_CHOICE=tea
><> deis ps:scale web=2
Scaling processes... but first, tea!
404 NOT FOUND
Detail:
Not found
```