[Modify] Polish it

websocket-sharp/Server/WebSocketBehavior.cs

@@ -351,7 +351,7 @@ namespace WebSocketSharp.Server
     internal void Start (WebSocketContext context, WebSocketSessionManager sessions)
     {
       if (_websocket != null) {
-        _websocket.Log.Error ("This session has already been started.");
+        _websocket.Log.Error ("A session instance cannot be reused.");
         context.WebSocket.Close (HttpStatusCode.ServiceUnavailable);
 
         return;