Install error in 1.1.17+ under python2.7

This line seems to break `pip install bitcoin` in 1.1.17 and onward. I'm using python2.7
https://github.com/vbuterin/pybitcointools/blame/master/setup.py#L14

https://gist.github.com/patcon/755e37cb57b588d29d6a

I believe pyethereum was working on python2.7 prior, but now its not

Also, you willing to accept a PR for travis support?