Generate DMG with travis as well
Summary: Use travis to generate a dmg file
Test Plan:
Running on travis via my github fork
https://travis-ci.org/sithlord48/atcore/builds/301520119
Reviewers: laysrodrigues, patrickelectric, tcanabrava
Reviewed By: patrickelectric, tcanabrava
Subscribers: Atelier: AtCore
Differential Revision: https://phabricator.kde.org/D8680