Update DiagnosticExtensions.cs

Author: ENikS

src/Extensions/DiagnosticExtensions.cs

@@ -1,16 +1,17 @@
-using System;
+using System;
 using System.Diagnostics;
 
 namespace Unity
 {
     public static class DiagnosticExtensions
     {
         [Conditional("DEBUG")]
-        public static void EnableDiagnostic(this UnityContainer container)
+        public static UnityContainer EnableDiagnostic(this UnityContainer container)
         {
             if (null == container) throw new ArgumentNullException(nameof(container));
 
             container.AddExtension(new Diagnostic());
+            return container;
         }
     }
 }