Bump Hatchet Dependency

- Hatchet now raises an error on failure, must flag `allow_failure: true` if you expect a failure on builds.
- Hatchet no longer masks `Anvil::Builder::BuildError` exceptions
- Hatchet::App#push! for both Git and Anvil now returns just an output string. On failures an exception will be raised
Hatchet knows how to set itself up on Travis CI

Run `bundle exec rake hatchet:setup_travis` instead of manually running each command
Merge pull request #101 from heroku/schneems/rev-hatchet

Update Hatchet