Support Custom Post Types

I needed this to work on a Custom Post Type I created, so I manually changed the meta_boxes method on admin/class-wp-terms-popup-admin.php file (line 164) and added my CPT there. It worked flawlessly. But that mean I’ll lose my change in the next update.

My suggestion is that you add a filter to that $screen variable, so devs can add more CPTs without having to directly change the plugin’s core.