Currently, all PRs are tested by Coveralls and Travis CI. Travis CI doesn't comment on our PRs, but Coveralls does. Initially, maybe, there wasn't a good way for Coveralls to indicate success/failure otherwise. However, since both Coveralls and Travis have the "tests in progress" section on the PR, every PR will show the latest Coveralls state right above the merge button.
So, I propose we stop Coveralls from generating these comments.