Add active class to active 'li' in Drupal 8 menus

THEMENAME.theme

function THEMENAME_preprocess_menu(&$variables, $hook) {
	if ($hook == 'menu_main') {
		THEMENAME_menu_active_item($variables['items']);
	}
}

function THEMENAME_menu_active_item(&$items) {
	$current_path = \Drupal::request()->getRequestUri();
	foreach ($items as $key => $item) {
		// if path is current path, set active to li
		if ($item['url']->toString() == $current_path) {
			// add active linl
			$items[$key]['attributes']['class'] = 'active';
		}
		if (!empty($items[$key]['below'])) {
			THEMENAME_menu_active_item($items[$key]['below']);
		}
	}
}

I'm working on twig template for bootstrap. can you please post twig code for this same.