Abort integration if a new commit is created during integration

Closes #36

What do you think @rafaelp @marcioj @eduardofiorezi @TiuTalk @mauro?
It is not a safe choice because jumpup:finish can be after jumpup:heroku:finish (which deploys to heroku and than verifies if it has a new commit).
In fact, jumpup-heroku readme changed the order to be `jumpup:heroku:finish` and than `jumpup:finish` https://github.com/Helabs/jumpup-heroku/commit/0fc90ae24cae9276aa24c00f021815ce940f8014