[Modify] Polish it

websocket-sharp/WebSocket.cs

@@ -1141,8 +1141,8 @@ namespace WebSocketSharp
         OnClose.Emit (this, e);
       }
       catch (Exception ex) {
-        _logger.Error (ex.ToString ());
+        _logger.Error (ex.Message);
-        error ("An error has occurred during the OnClose event.", ex);
+        _logger.Debug (ex.ToString ());
       }
     }