Updated tox and Travis to use py36.

- Added a matrix config to Travis to align tox an travis environments.
- Locked dist to trusty

.travis.yml

@@ -1,9 +1,13 @@
+dist: trusty
 language: python
 
 sudo: false
-env:
-    - TOXENV=py27
-    - TOXENV=py34
+matrix:
+    include:
+        - python: 2.7
+          env: TOXENV=py27
+        - python: 3.6
+          env: TOXENV=py36
 
 install:
     - travis_retry pip install tox

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py34
+envlist = py27,py36
 
 [testenv]
 commands=python test_httpbin.py