travis: Only notify IRC about failures on change

There's no need to notify IRC on every failure, it can get spammy when
we're iterating trying to fix something.

This patch changes the config to notify IRC on change instead of always.

.travis.yml

@@ -42,4 +42,4 @@ notifications:
           - "ircs://chat.freenode.net:7070/#chasquid"
         use_notice: true
         on_success: change
-        on_failure: always
+        on_failure: change