Change Pro manual booking user dropdown to show usernames

<?php
/*
This snippet changes the dropdown for selecting a user for adding a booking manually to show usernames instead of their full name.

for more information on adding this snippet to your site, see here
http://wp-events-plugin.com/tutorials/how-to-safely-add-php-code-to-wordpress/
*/
function my_em_mod_change_manual_booking_userddm(){
    add_filter('em_locate_template', function( $located, $template_name ){
        if( $template_name == 'placeholders/bookingform.php'){
            remove_action('em_booking_form_custom', array(EM_Gateways::get_gateway('offline'),'em_booking_form_custom'), 1);
            add_action('em_booking_form_custom', 'my_offline_em_booking_form_custom', 1);
        }
        return $located;
    }, 10, 2);
}
add_action('em_bookings_manual_booking', 'my_em_mod_change_manual_booking_userddm', 1);

function my_offline_em_booking_form_custom(){
    ?>
    <p>
        <?php
            $person_id = (!empty($_REQUEST['person_id'])) ? $_REQUEST['person_id'] : false;
            wp_dropdown_users ( array ('name' => 'person_id', 'show' => 'user_login', 'show_option_none' => __ ( "Selectxxx a user, or enter a new one below.", 'em-pro' ), 'selected' => $person_id  ) );
        ?>
    </p>
    <?php
}