test with Python 3.8 on appveyor

Author: mr-c

appveyor.yml

@@ -20,6 +20,10 @@ environment:
       PYTHON_VERSION: "3.7.x"
       PYTHON_ARCH: "64"
 
+    - PYTHON: "C:\\Python38-x64"
+      PYTHON_VERSION: "3.8.x"
+      PYTHON_ARCH: "64"
+
 install:
   - ps: 'Install-Product node 0.12 x64'
   - "set PATH=%PYTHON%\\Scripts;%PATH%"