.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.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62361 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.travis.yml

@@ -88,7 +88,8 @@ notifications:
 
   slack:
     rooms:
-      secure: ah7UEHBvncXT7bM5mvYIQAO+tIyV/wl7nXLb7wQD16dO2v8Gragy0mWjB79Q09hrrMGmp6H9bCDpdGS80boIA5EHaHoG4QaP0i9bsSt8U2AMWgZtfyIgQKJ4H2kXkGlrjO+AXTgnIkP7LNjdgAVUUTGQPb26T3QmoN2Splt+fIQ= # ruby:<token>#alerts
+      - secure: i1GLETSKye85ea6dGNA3MxI/5myChmMFiZtBd5C69xK+s1sBFqEgOSbaSf9KHc0CYrHVyNhQMaZRruieV7xS+6Pfs0Zvxf1DO6QQTWC2KhkqwFDLvZncAzjoyASdR90hbr+iRPOngQ+HJuE94zemALAwEqNAinzA74PMiJXktqY= # ruby:<token>#commits
+      - secure: ah7UEHBvncXT7bM5mvYIQAO+tIyV/wl7nXLb7wQD16dO2v8Gragy0mWjB79Q09hrrMGmp6H9bCDpdGS80boIA5EHaHoG4QaP0i9bsSt8U2AMWgZtfyIgQKJ4H2kXkGlrjO+AXTgnIkP7LNjdgAVUUTGQPb26T3QmoN2Splt+fIQ= # ruby:<token>#alerts
     on_pull_requests: false
     on_success: change
     on_failure: always