fix unit tests.

build/XUnit.props

@@ -1,14 +1,14 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="xunit" Version="2.3.0" />
-    <PackageReference Include="xunit.abstractions" Version="2.0.1" />
-    <PackageReference Include="xunit.assert" Version="2.3.0" />
-    <PackageReference Include="xunit.core" Version="2.3.0" />
-    <PackageReference Include="xunit.extensibility.core" Version="2.3.0" />
-    <PackageReference Include="xunit.extensibility.execution" Version="2.3.0" />
-    <PackageReference Include="xunit.runner.console" Version="2.3.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0" />
-    <PackageReference Include="Xunit.SkippableFact" Version="1.3.6" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.abstractions" Version="2.0.3" />
+    <PackageReference Include="xunit.assert" Version="2.4.1" />
+    <PackageReference Include="xunit.core" Version="2.4.1" />
+    <PackageReference Include="xunit.extensibility.core" Version="2.4.1" />
+    <PackageReference Include="xunit.extensibility.execution" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.console" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
   </ItemGroup>
   <PropertyGroup>