Added test runner for VS

DOCXTests/DOCXTests.csproj

@@ -9,7 +9,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0-preview-20170628-02" />
         <PackageReference Include="xunit" Version="2.2.0" />
-        <PackageReference Include="xunit.runner.visualstudio" Version="2.2.0" />
+        <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />
     </ItemGroup>
 
     <ItemGroup>