bringing back needed reference

Author: ritamerkl

Assets/Tests/InputSystem/DocumentationBasedAPIVerficationTests.cs

@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Text;
 using HtmlAgilityPack;
 using Mono.Cecil;