Put this in your functions.php:
function additional_active_item_classes($classes = array(), $menu_item = false){
global $wp_query;
if(in_array('current-menu-item', $menu_item->classes)){
$classes[] = 'current-menu-item';
}
if ( $menu_item->post_name == 'product' && is_post_type_archive('product') ) {
$classes[] = 'current-menu-item';
}
if ( $menu_item->post_name == 'product' && is_singular('product') ) {
$classes[] = 'current-menu-item';
}
return $classes;
}
add_filter( 'nav_menu_css_class', 'additional_active_item_classes', 10, 2 );
This code check if you are on a page product archive or an single product and if so it adds the class current-menu-item