http://danielpataki.com/2013/04/standardizing-wordpress-menus/

standard_menu.php

<?php

function bs_nav_menu(){
  $menu = wp_page_menu( array(
		'menu_class' => 'menu-container',
		'echo'       => false
	));

	$menu = str_replace(
		array(
			'current_page_item',
			'current_page_parent',
			'current_page_ancestor',
			'<ul>',
			'page_item',
			'<ul class=\'children\'>'
		),
		array(
			'current-menu-item',
			'current-menu-parent',
			'current-menu-ancestor',
			'<ul class="menu">',
			'menu-item',
			'<ul class="sub-menu">'
		),
		$menu
	);

	echo $menu;
}

?>