@guysv sorry for the silence! I have to go, but I'll give it a look when I get the chance. The travis failure is that pip has dropped support for Python 3.3, but the initial pip on travis (8) doesn't have support for the requires-python directive.
You can add a conditional install of pip install pip==10.* on python 3.3 prior to the pip install --upgrade, and I think it will be okay. I can help with this later, if you'd like.