Fix due to the added HttpServer

Example3/Echo.cs

@@ -0,0 +1,19 @@
+using System;
+using WebSocketSharp;
+using WebSocketSharp.Server;
+
+namespace Example3
+{
+  public class Echo : WebSocketService
+  {
+    protected override void onMessage(object sender, MessageEventArgs e)
+    {
+      Send(e.Data);
+    }
+
+    protected override void onClose(object sender, CloseEventArgs e)
+    {
+      Console.WriteLine("[Echo] Close({0}: {1})", (ushort)e.Code, e.Code);
+    }
+  }
+}