Add span tag around WordPress menu item

functions.php

<?php

/**
 * Add span to menu items with icon class so we can hide the text and show icons instead
 *
 * @link http://codex.wordpress.org/Function_Reference/wp_get_nav_menu_items
 */
add_filter( 'walker_nav_menu_start_el', 'hrt_span_to_nav_menu', 10, 4 );
function hrt_span_to_nav_menu( $item_output, $item, $depth, $args ) {
	if ( isset( $item->classes ) && !empty( $item->classes ) ) {
		if ( in_array( 'icon-twitter', (array) $item->classes ) || in_array( 'icon-linkedin', (array) $item->classes ) ) {
			$item_output = '<span><a href="'. $item->url .'" title="'. $item->attr_title .'"></a></span>';
		}
	}

	return $item_output;
}