Update python versions

Author: laurynas

.travis.yml

@@ -1,13 +1,12 @@
 language: python
 python:
-- 2.6
 - 2.7
-- 3.3
 - 3.4
 - 3.5
 - 3.6
+- 3.7
+- 3.8
 install:
-- if [[ $TRAVIS_PYTHON_VERSION == 2.6 ]]; then pip install importlib unittest2; fi
 - pip install -r requirements.txt
 - pip install -r test-requirements.txt
 - python setup.py develop