Add python 3.6 to appveyor config

appveyor.yml

@@ -13,6 +13,9 @@ environment:
     - PYTHON: "C:\\Python35"
       TOXENV: "py35"
+    - PYTHON: "C:\\Python36"
+      TOXENV: "py36"
+
 init:
   - ps: echo $env:TOXENV
   - ps: ls C:\Python*