Add more windows builds

Author: echu

appveyor.yml

@@ -7,11 +7,17 @@ environment:
     - PYTHON: "C:\\Python34"
     - PYTHON: "C:\\Python35"
     - PYTHON: "C:\\Python36"
+    - PYTHON: "C:\\Python37"
+    - PYTHON: "C:\\Python38"
+    - PYTHON: "C:\\Python39"
     #- PYTHON: "C:\\Python27-x64"
     - PYTHON: "C:\\Python34-x64"
       DISTUTILS_USE_SDK: "1"
     - PYTHON: "C:\\Python35-x64"
     - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37-x64"
+    - PYTHON: "C:\\Python38-x64"
+    - PYTHON: "C:\\Python39-x64"
 
 install:
   # initialize the submodule