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) code example
Example: PHP Fatal error: Class UpdateHelper\ComposerPlugin contains 2 abstract methods and must therefore be declared abstract or implement the remaining methods (Composer\Plugin\PluginInterface::deactivate
composer update kylekatarnls/update-helper
composer update --prefer-source