Fix error in selector in inValid() method

Was getting error in example included in the plugin. During debugging found problem with below code in invalid() method:

    selector = (selector == 'id'
                ? '#' + attr
                : '[' + selector + '=' + attr + ']');
    var control = view.$('[' + selector + '=' + attr + ']');

Made the necessary changes with selector now so please review and do the needful accordingly.

    selector = (selector == 'id'
                ? '#' + attr
                : '[' + selector + '=' + attr + ']');
    var control = view.$(selector);