twitter-oss: Add Slack notification configuration to TravisCI
twitter-oss: Add Slack notification configuration to TravisCI

Summary: Problem/Solution

Move from Hipchat to Slack TravisCI notifications for:
util, scrooge, finagle, twitter-server, and finatra.

Differential Revision: https://phabricator.twitter.biz/D121452

twitter/util,twitter/util,twitter/util