Add python versions for Travis CI
diff --git a/.travis.yml b/.travis.yml
index de6e87b..fea2644 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,7 @@
 language: python
+python:
+  - "2.7"
+  - "3.5"
 
 env:
   - TOX_ENV=pep8