Update Travis matrix to reflect supported versions

Author: gtaylor

.travis.yml

@@ -1,8 +1,8 @@
 language: python
 python:
   - "2.7"
-  - "3.3"
-  - "3.4"
+  - "3.5"
+  - "3.6"
 # command to install dependencies
 install: "pip install -r requirements.txt"
 # command to run tests