Travis notifications are disabled (https://github.com/moodle/moodle/blob/master/.travis.yml#L7) with the following comment:

1. We currently disable Travis notifications entirely until https://github.com/travis-ci/travis-ci/issues/4976
2. is fixed.

That issue has been fixed, https://github.com/travis-ci/travis-ci/issues/4976, so we should remove this comment and enable notifications or keep notifications disabled and modify the comment.