Update tox.ini so we can slowly move over to tox from make

We are not compatible with python3.4 because of one of our dependencies. (gitpython -> gitdb). [Ref: https://github.com/gitpython-developers/gitdb/pull/13]

We are not compatible with 2.6 either. I am unsure how travis builds 2.6 just fine. Doesn't pass on my local box.