Change windows and vs version.

Author: ericmjl

.azure-pipelines/azure-pipelines.yml

@@ -45,7 +45,7 @@ jobs:
         py36:
           python.version: "3.6"
     pool:
-      vmImage: windows-2019
+      vmImage: vs2017-win2016
     steps:
       # https://docs.microsoft.com/en-us/azure/devops/pipelines/languages/anaconda?view=azure-devops&tabs=vs2017
       - powershell: Write-Host "##vso[task.prependpath]$env:CONDA\Scripts"