fix error in navList with TbHtml::menuDivider()

Hi. Sorry for my English:)
In the example from http://www.getyiistrap.com/site/components#navs
```php
<?php echo TbHtml::navList(array(
        array('label' => 'List header'),
        array('label' => 'Home', 'url' => '#', 'active' => true),
        array('label' => 'Library', 'url' => '#'),
        array('label' => 'Applications', 'url' => '#'),
        array('label' => 'Another list header'),
        array('label' => 'Profile', 'url' => '#'),
        array('label' => 'Settings', 'url' => '#'),
        TbHtml::menuDivider(),
        array('label' => 'Help', 'url' => '#'),
    )); ?>
```
Error 
```php
ErrorException: Argument 2 passed to TbArray::popValue() must be of the type array, string given, called in /home/karneds/www/yiistrap/helpers/TbHtml.php on line 2973 and defined
```