py3.6

[kaylanb]

py2.7 --> py3.6

• https://docs.python.org/3/howto/pyporting.html
• http://python-future.org/automatic_conversion.html#step-2-working-py3-code-that-still-supports-py2

[kaylanb]

done, travis test case only does 2.7 because it takes so long to build the software stack, but both 3.6 and 2.7 work