<?php
/*  TGM plugin activation
/* ------------------------------------ */
require_once('/class-tgm-plugin-activation.php');

if ( ! function_exists( 'alx_plugins' ) ) {
    function my_theme_register_required_plugins() {
        // Add the following plugins
        $plugins = array(
            array(
                'name' => 'Post Thumbnail Editor',
                'slug' => 'post-thumbnail-editor',
                'required' => false,
            ),
        );
        tgmpa($plugins);
    }
}

add_action('tgmpa_register', 'my_theme_register_required_plugins');