Add NetStandard test assembly to SkipStrongNames.xml

Author: dougbu

tools/SkipStrongNames.xml

@@ -42,6 +42,7 @@
   <assembly name="System.Json.Test.Integration"/>
   <assembly name="System.Net.Http.Formatting.Test"/>
   <assembly name="System.Net.Http.Formatting.NetCore.Test"/>
+  <assembly name="System.Net.Http.Formatting.NetStandard.Test"/>
   <assembly name="System.Net.Http.Formatting.Test.Integration"/>
   <assembly name="System.Web.Cors.Test"/>
   <assembly name="System.Web.Helpers.Test"/>