Try to fix Travis CI configuration.
.travis.yml: send notification to #alerts
instead of #commits.
.travis.yml: resurrect notification to #commits
I heard at least Shibata-san sees the channel for the notification.
But I want #alets to have all CI failure notifications too.
merge revision(s) 61605,62359,62361: [Backport #14356]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@62537 b2dd03c8-39d4-4d8f-98ff-823fe69b080e