[twit] Python 2 should use unicode(), not str()

The twit module was tripping on users with Unicode characters in their profile data, and Python 2.x distinguishes between `str` and `unicode` as different types (yes, yes, upgrade to Py3, etc.).

I *think* this is a decent way of doing it, but please tell me if there's a better way to fix this and keep compatibility with both Py2 & Py3.