Update IRC channel in CONTRIBUTING.md
Contributing just involves sending a pull request. You will probably be more
successful with your contribution if you visit the [IRC
-channel](http://webchat.freenode.net/?channels=sway&uio=d4) upfront and discuss
+channel](http://webchat.freenode.net/?channels=sway-devel&uio=d4) upfront and discuss
your plans.
## Pull Requests
