REL: add Trove classifiers for Python 3.4, 3.5, 3.6
REL: add Trove classifiers for Python 3.4, 3.5, 3.6

Addition of these classifiers signifies support of
these Python versions, so this change is ordered after
testing with these Python versions on Travis CI.

tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control