Fixup sample (#12880)

aspnetcore/tutorials/signalr-typescript-webpack/sample/Hubs/ChatHub.cs

@@ -5,7 +5,7 @@ namespace SignalRWebPack.Hubs
 {
     public class ChatHub : Hub
     {
-        public async Task NewMessage(string username, string message)
+        public async Task NewMessage(long username, string message)
         {
             await Clients.All.SendAsync("messageReceived", username, message);
         }