Fix bug in URI regex

URI regex used to match invalid strings like "hey...got" and prepend
an "http://" in inappropriate places.

The regex could still use some work.  For example, it will match
things like "hi.how" and even rarer things like "queen.latifah".
But for now, I can chat with my girlfriend without seemingly
random "http://"s popping up.
Merge pull request #31 from baguette/master

Fix bug in URI regex