Automatically cancel PR builds when PRs are closed or merged.

[ghost]

No description provided.

[CryptAxe]

This is a good idea 👍

[mozeryansky]

The scenario we run into a lot is someone approving the PR with a minor request, like changing a word or two, something that definitely won't break a build (to our best knowledge). So instead of waiting for it to build before merging, we would make the change, push, and have GitHub merge. This spins off a new build which immediately fails. Now our repo is marked as "Job Errored".

In the meantime, is there a way to have Travis cancel the job while the job is running?