Specify .netcore version to 2.1 for msvc2019

Author: buresu

azure-pipelines.yml

@@ -258,6 +258,12 @@ jobs:
       }
     displayName: 'Create placeholder depth engine'
 
+  - task: UseDotNet@2
+    inputs:
+      packageType: 'sdk'
+      version: '2.1.x'
+    condition: and(succeeded(), eq(variables['vmImage'], 'windows-2019'))
+
   - task: NuGetToolInstaller@0
     inputs:
       versionSpec: '>=4.3.1'