add python 3.6 testing

Author: pseewald

.travis.yml

@@ -3,6 +3,7 @@ python:
  - 2.7
  - 3.4
  - 3.5
+ - 3.6
 before_install:
  - if [[ $TRAVIS_PYTHON_VERSION == "2.7" ]] || [[ $TRAVIS_PYTHON_VERSION == "3.5" ]]; then export DO_COVERAGE=1; fi
  - if [[ "$TRAVIS_EVENT_TYPE" = "cron" ]]; then unset DO_COVERAGE; fi