Deprecated Method in wp-stats.php

Hi. I’m using Query Monitor (a plugin by John Blackbourn, you can easily find in WP Plugin repository) to debug my site and it reported me that WP-UserOnline uses a deprecated method to define a class.
This is the warning about a class in file wp-stats.php: “Non-static method UserOnline_WpStats::init() should not be called statically”.
Hi.
dario

P.S. Thank you @gamerz for your contribution in developing plugins for so many years!