Notify the public room on deploy as well

... since we get GitHub notifications there, and it's useful to see deploy
notifications interleaved with what's happening on GitHub.

Resolves #79

Test plan: Ran `PYTHONPATH=.. python notify_deploy.py 'david test'` with the
room ID of a private test room for `HIPCHAT_PUBLIC_ROOM_ID`.
Merge pull request #101 from UWFlow/david-deploy-notify-public-room

Notify the public room on deploy as well