Update win_python38 build

Author: ijl

ci/azure-pipelines.yml

@@ -131,7 +131,7 @@ jobs:
   pool:
     vmImage: vs2017-win2016
   variables:
-    interpreter: C:\hostedtoolcache\windows\Python\3.8.0\x64\python.exe
+    interpreter: C:\hostedtoolcache\windows\Python\3.8.1\x64\python.exe
     target: x86_64-pc-windows-msvc
   steps:
   - task: UsePythonVersion@0