v1.0-BETA-5 has reference to classes in Gravity Forms plugin which break install

New lines were added which reference the GFCommon class of the Gravity Forms plugin, which may not yet exist.

For example, in the install function of class-gf-cli-root.php on line 103, the following is present:

$key = GFCommon::get_key();

However, as this is at the start of the install function, the Gravity Forms plugin files have not yet been downloaded, and so a PHP fatal error is thrown due to the class not being found.