Update when post is edited

Using the example:

add_filter( 'slack_get_events', function( $events ) {
    $events['post_updated_rc'] = array(
        'action'      => 'post_updated',
        'description' => __( 'When a post is updated', 'slack' ),
        'message'     => function( $post ) {
            return sprintf( '%s updated', $post );
        }

The docs are a little light on thing but post_updated seems to be the correct action hook. Anyone else alive who has gotten this to work?

https://wordpress.org/plugins/slack/