help python development by testing 3.6-dev

.travis.yml

@@ -25,6 +25,10 @@ matrix:
           os: linux
           dist: trusty
           env: TOXENV=flake8
+        - python: "3.6-dev"
+          os: linux
+          dist: trusty
+          env: TOXENV=py36
         - language: generic
           os: osx
           osx_image: xcode6.4