Added using for DataMember filter

ChuckSavage · ChuckSavage · commit 4dff2a491000 · 2012-08-09T12:52:58.000-06:00
diff --git a/src/ServiceStack.ServiceInterface/Auth/AuthService.cs b/src/ServiceStack.ServiceInterface/Auth/AuthService.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Configuration;
 using System.Linq;
+using System.Runtime.Serialization;
 using ServiceStack.Common.Utils;
 using ServiceStack.Common.Web;
 using ServiceStack.ServiceHost;
