use Python 3.6

[MikeBadescu]

Problem:

• This version uses Python 2.7 and rpy2==2.8.4

Solution:

• Switch to Python 3.6

TODO:

• [ ] install Python 3.6, pip3, update pip, install rp2 for python 3
• [ ] make it work / test with R 3.4.x

[MikeBadescu]

seems to be working OK