Error in wp-mailinglist-plugin.php trying to activate plugin

I've uploaded Newsletter plugin version 4.6.4.1 to my WP site but it fails to activate with the following error.

Parse error: syntax error, unexpected T_STRING in /my/path/public_html/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php on line 2107

This is the line the error refers to:
$mg = new Mailgun\Mailgun($mailgun_apikey);

What might be causing this?