Fixed setup.py to work with newer versions of pip

Apparently Pip req.parse_requirements is not supposed to be called from outside pip, they're moving it in next version and had already changed it, breaking your setup.py.

source: Pip maintainers comment here: http://stackoverflow.com/questions/14399534/how-can-i-reference-requirements-txt-for-the-install-requires-kwarg-in-setuptool