[Modify] Polish it

websocket-sharp/Server/WebSocketSessionManager.cs

@@ -887,8 +887,10 @@ namespace WebSocketSharp.Server
     public void CloseSession (string id)
     {
       IWebSocketSession session;
+
       if (!TryGetSession (id, out session)) {
         var msg = "The session could not be found.";
+
         throw new InvalidOperationException (msg);
       }