Update travis.yml

Author: tk0miya

.travis.yml

@@ -1,15 +1,13 @@
 language: python
-python: 3.5
-env:
-  matrix:
-    - TOXENV=py26
-    - TOXENV=py27
-    - TOXENV=py33
-    - TOXENV=py34
-    - TOXENV=py35
-    - TOXENV=coverage
+python:
+  - 2.7
+  - 3.4
+  - 3.5
+  - 3.6
 cache:
   directories:
     - $HOME/.cache/pip
-install: pip install docutils tox
-script: tox
+install: pip install docutils tox tox-travis
+script:
+  - tox
+  - if [[ $TRAVIS_PYTHON_VERSION == '3.6' ]]; then tox coverage; fi