Test against Python 3.7 on AppVeyor

Author: RazerM

.appveyor.yml

@@ -12,6 +12,8 @@ environment:
     - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36"
     - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37"
+    - PYTHON: "C:\\Python37-x64"
 
 build_script:
   - "git --no-pager log -n2"