Add colorbox to the lightbox array in Easy Image Gallery

gistfile1.php

<?php

function my_theme_easy_image_gallery_lightbox( $lightboxes ) {
    // the option that is saved to the database, and the label that appears in the select menu
    $lightboxes['colorbox'] = 'Colorbox';
    return $lightboxes;
}
add_filter( 'easy_image_gallery_lightbox', 'my_theme_easy_image_gallery_lightbox' );