Run tests on Python 3.3

Author: alanhamlett

.travis.yml

@@ -4,11 +4,12 @@ matrix:
     - python: 2.6
       dist: trusty
     - python: 2.7
+    - python: 3.3
+      dist: trusty
     - python: 3.4
     - python: 3.5
     - python: 3.6
     - python: 3.7
-      dist: xenial
       sudo: true
 install:
     - if [[ $TRAVIS_PYTHON_VERSION != '2.6' ]]; then travis_retry pip install coveralls; fi