In reply to Sarah Gooding.

No license info yet, nor in their website or in the downloaded plugin .zip file or in their plugin meta info, which is exactly as below:

/*
Plugin Name: WP Rocket
Plugin URI: http://www.wp-rocket.me
Description: The best WordPress performance plugin.
Version: 2.6.4
Code Name: Yavin
Author: WP Rocket
Contributors: Jonathan Buttigieg, Julio Potier
Author URI: http://www.wp-rocket.me

Text Domain: rocket
Domain Path: languages

Copyright 2013-2015 WP Rocket
*/

So, where is Matt?