fixed #82 made active signature and active parameter nullable

Author: david-driscoll

src/Protocol/Models/SignatureHelp.cs

@@ -20,12 +20,12 @@ public class SignatureHelp
         /// The active signature.
         /// </summary>
         [Optional]
-        public int ActiveSignature { get; set; }
+        public int? ActiveSignature { get; set; }
 
         /// <summary>
         /// The active parameter of the active signature.
         /// </summary>
         [Optional]
-        public int ActiveParameter { get; set; }
+        public int? ActiveParameter { get; set; }
     }
 }