Get rid of "joined/left" messages on Travis Build.

The default behaviour of the IRC notification is
pretty noisy, therefore get rid of "joined/left"
messages by the Bot joining before posting and
on leaving the channel.
Furthermore propagate only Failed builds and
transition from previous build state.
Merge remote-tracking branch 'upstream/master'
Always notify IRC on Travis Build.
Merge pull request #68 from h5b/master

Avoid "joined/left" messages on Travis Build Notification on IRC