Add integration to um-csg Slack #notifications channel for Travis CI builds

[Frencil]

This change makes it so Travis CI builds will show up in the um-csg #notifications channel on Slack. Submitted as a pull req since I haven't been doing any production work on this repo yet.

The token is the same used for locuszoom's travis/slack integration because they're going to the same place, so there only needs to be one integration record (and therefore one token) in our slack settings.