update test sdk

Author: Oren Novotny

Rx.NET/Source/tests/Tests.System.Reactive/Tests.System.Reactive.csproj

@@ -17,7 +17,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.0.0-preview-20181205-02" />    
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.0.1" />    
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />
     <ProjectReference Include="..\..\src\System.Reactive\System.Reactive.csproj" />