meta: Fix .NET Core 3.0 compatibility + Drop NS1.3 (#1382)

* Update all dependencies and deal with warning/errors

* Add updated AsyncEnumerable implementation

* Fix broken target

* Cleanup

* Remove obsolete message

* typo

* Update azure pipelines

* Update samples to .NET Core 3.0

* Pull out test change

* Install the .net core 3 SDK on the ubuntu image for the time being

* Target net core 3 for the unit tests because pipelines

azure-pipelines.yml

@@ -16,18 +16,23 @@ jobs:
   pool:
     vmImage: 'ubuntu-16.04'
   steps:
+  - task: UseDotNet@2
+    displayName: 'Use .NET Core sdk'
+    inputs:
+      packageType: 'sdk'
+      version: '3.x'
   - template: azure/build.yml
 
 - job: Windows_build
   pool:
-    vmImage: 'vs2017-win2016'
+    vmImage: 'windows-2019'
   condition: ne(variables['Build.SourceBranch'], 'refs/heads/dev')
   steps:
   - template: azure/build.yml
 
 - job: Windows_deploy
   pool:
-    vmImage: 'vs2017-win2016'
+    vmImage: 'windows-2019'
   condition: |
       and (
         succeeded(),