Update .travis.yml

Author: bjinwright

.travis.yml

@@ -1,10 +1,7 @@
 language: python
 python:
-  - "2.7"
-  - "3.3"
-  - "3.4"
   - "3.5"
-  - "3.5-dev" # 3.5 development branch
+  - "3.6" # 3.5 development branch
 # command to install dependencies
 install: "pip install -r requirements.txt"
 # command to run tests