expose the getter of open in WebsocketConnection so it can be used from outside the lib

Author: rinick

lib/src/browser/browser_ws_conn.dart

@@ -78,6 +78,8 @@ class WebSocketConnection extends Connection {
   }
 
   bool _opened = false;
+  bool get opened => _opened;
+
   void _onOpen(Event e) {
     logger.info("Connected");
     _opened = true;