(GH-150) Update Microsoft.NET.Test.Sdk to 17.8.0

* fixes #150

Author: devlead

test/LitJSON.Tests.csproj

@@ -9,7 +9,7 @@
   <ItemGroup>
     <PackageReference Include="nunit" Version="3.9.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.9.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
   </ItemGroup>
 
   <ItemGroup>