Composer dump-autoload or update results in fatal error on Laravel 5.5

Just tried to run a composer dum-autoload, but ended up with the following error, which I have never had previously

Class UpdateHelper\ComposerPlugin contains 2 abstract methods and must therefore be declared abstract or implement the remaining methods (Composer\Plugin\PluginInterface::deactivate, Composer\Plugin\PluginInterface::uninstall) in /var/www/vhosts/example.com/vendor/kylekatarnls/update-helper/src/UpdateHelper/ComposerPlugin.php on line 11

Searched on G to find some answers, but found nothing even remotely close the problem I am having here.

Any suggestions?

via Chebli Mohamed