Updated test sdk

Author: niemyjski

tests/Directory.Build.props

@@ -6,7 +6,7 @@
     <NoWarn>$(NoWarn);CS1591;NU1701</NoWarn>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />