Merge pull request buildbot#6613 from p12tic/reduce-appveyor-builds

appveyor: Reduce the number of Python versions tested on Appveyor to 1

Author: p12tic

appveyor.yml

@@ -8,8 +8,6 @@ environment:
   matrix:
     # For Python versions available on AppVeyor, see
     # http://www.appveyor.com/docs/installed-software#python
-    - PYTHON: "C:\\Python37"
-    - PYTHON: "C:\\Python38"
     - PYTHON: "C:\\Python39"
 
 install: