message: appveyor use Python3.9-x64
diff: @@ -11,7 +11,7 @@ environment:
  # Visual Studio 2019 x64
  - GENERATOR: Visual Studio 16 2019
  BUILD_TYPE: Release
  - PYTHON: "C:\\Python37-x64"
  + PYTHON: "C:\\Python39-x64"
  # add to path otherwise Cython is not found
  PATH: $(PYTHON)\Scripts;$(PATH)
  PLATFORM: x64
  