Unary typeof bug

This is a PR based upon https://github.com/millermedeiros/esformatter/pull/148
This code change should also fix https://github.com/rdio/jsfmt/issues/6

I'm not sure if this handles all corner cases, but it fixes the mentioned bugs.
Very nice project, I really didn't need much time to find out how to change the observed behavior. Also thanks to @jzaefferer for the failing test which helped a lot.