refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -16,7 +16,7 @@
     <PackageVersion Include="Microsoft.Bcl.AsyncInterfaces" Version="9.0.0" />
     <PackageVersion Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.4" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp" Version="4.9.2" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageVersion Include="NUnit" Version="4.2.2" />
     <PackageVersion Include="MSTest" Version="3.6.3" />
     <PackageVersion Include="MSTest.TestFramework" Version="3.6.3" />