fix(XmppConnection): the ATTACHED state equals to CONNECTED with jiconop

When Jiconop is used to attach to a warmed up BOSH session Strophe goes
to ATTACHED instead of the CONNECTED state.

modules/xmpp/XmppConnection.js

      * @returns {boolean}
      */
     get connected() {
-        return this._status === Strophe.Status.CONNECTED;
+        return this._status === Strophe.Status.CONNECTED || this._status === Strophe.Status.ATTACHED;
     }
 
     /**