I'm using bootstrap in my theme, so I have a requirement that I add a class of `active` to the current nav menu item.

I was able to achieve this by using the `nav_menu_css_class` filter

    add_filter('nav_menu_css_class' , 'special_nav_class' , 10 , 2);
    function special_nav_class($classes, $item){
         if( in_array('current-menu-item', $classes) ){
                 $classes[] = 'active ';
         }
         return $classes;
    }

The problem is, say the current page is 'about' -> 'locations'

then the 'about' nav menu looses its 'active' class because obviously it is no longer the 
`current-menu-item` but I also need it to have the 'active' class if I'm viewing one of its child pages

How would I go about solving this?