the cron info array to version 2.
 *
 * @since 2.1.0
 * @access private
 *
 * @param array $cron Cron info array from _get_cron_array().
 * @return array An upgraded cron info array.
 */
function _upgrade_cron_array( $cron ) {
	if ( isset( $cron['version'] ) && 2 === $cron['version'] ) {
		return $cron;
	}

	$new_cron = array();

	foreach ( (array) $cron as $timestamp => $hooks ) {
		foreach ( (array) $hooks as $hook => $args ) {
			$key = md5( serialize( $args['args'] ) );

			$new_cron[ $timestamp ][ $hook ][ $key ] = $args;
		}
	}

	$new_cron['version'] = 2;

	update_option( 'cron', $new_cron, true );

	return $new_cron;
}