[Modify] Polish it

websocket-sharp/WebSocket.cs

@@ -2230,7 +2230,7 @@ namespace WebSocketSharp
       lock (_forSend) {
         lock (_forState) {
           if (_readyState != WebSocketState.Open) {
-            _logger.Error ("The state of the connection has been changed.");
+            _logger.Error ("The connection is closing.");
             return;
           }