update travis to run different python versions

Author: Kebniss

.travis.yml

@@ -1,15 +1,17 @@
 language: python
 python: 3.5
 sudo: false
-branches:
-    only:
-        - master
-        - /^\d\.\d+$/
-env:
-    - TOXENV=py27
-    - TOXENV=py34
-    - TOXENV=py35
-    - TOXENV=docs
+
+matrix:
+  include:
+    - python: 2.7
+      env: TOXENV=py27
+    - python: 3.4
+      env: TOXENV=py34
+    - python: 3.5
+      env: TOXENV=py35
+    - python: 3.6
+      env: TOXENV=py36
 
 addons:
     apt:
@@ -30,4 +32,4 @@ after_success:
 
 cache:
     directories:
-        - $HOME/.cache/pip
+        - $HOME/.cache/pip