PHP 8.0 compatibility

Hi,

I am currently working out how to achieve PHP 8.0 compatibility with this plugin. If there is enough interest in this, I might fork the repo to overhaul this plugin, since it is not updated for 4 years now.

To get the plugin running with PHP 8.0, I had to do the following changes:

nomad-world-map/includes/nwm-widget-class.php

//add_action( 'widgets_init',
//     create_function( '', 'return register_widget( "NWM_Widget" );' )
//);

add_action( 'widgets_init', function() {
     register_widget( 'NWM_Widget' );
});

nomad-world-map/admin/nwm-check-upgrade.php

//    if (version_compare($current_version, NWN_VERSION_NUM, '==='))
    if (version_compare($current_version, NWN_VERSION_NUM, '=='))

Good luck!