Use commit_subject for Travis IRC notifications

commit_message has newlines which break the rather naive
IRC client Travis uses

.travis.yml

@@ -32,4 +32,4 @@ notifications:
     channels:
       - "irc.freenode.org:6667#diaspora-dev"
     template:
-      - "%{repository_slug}#%{commit} (%{branch} - %{commit_message}): %{message} %{build_url}"
+      - "%{repository_slug}#%{commit} (%{branch} - %{commit_subject}): %{message} %{build_url}"