Uninstall error

On uninstall of the plugin from the plugins page I got this in the debug log:

[02-Jul-2020 04:14:33 UTC] PHP Warning: Use of undefined constant WP_UNINSTALL_PLUGIN – assumed ‘WP_UNINSTALL_PLUGIN’ (this will throw an Error in a future version of PHP) in /home/sites/public_html/mysite/wp-content/plugins/export-import-menus/main.php on line 43

Thanks for a great plugin!