Have appveyor test Py36/Py37

Author: digitalresistor

Diff for: appveyor.yml

@@ -1,13 +1,17 @@
 environment:
   matrix:
-    - PYTHON: "C:\\Python35"
-      TOXENV: "py35"
     - PYTHON: "C:\\Python27"
       TOXENV: "py27"
     - PYTHON: "C:\\Python27-x64"
       TOXENV: "py27"
-    - PYTHON: "C:\\Python35-x64"
-      TOXENV: "py35"
+    - PYTHON: "C:\\Python36"
+      TOXENV: "py36"
+    - PYTHON: "C:\\Python36-x64"
+      TOXENV: "py36"
+    - PYTHON: "C:\\Python37"
+      TOXENV: "py37"
+    - PYTHON: "C:\\Python37-x64"
+      TOXENV: "py37"
 
 cache:
     - '%LOCALAPPDATA%\pip\Cache'