Just an eensy-weensy bug fix in this one. Don’t bother to upgrade unless you know you need it.
If your screen-scraper was updated from a 2.7.x release, you can go ahead and just update in the usual manner (i.e., select “Check for updates…” from the “Options” menu).
If you installed a fresh copy of version 3.0, you’ll need to download the updater.jar file here, and copy it into your screen-scraper folder. After that you can update in the usual manner. Either that, or you can just re-download a version 3.0 installer, and install a fresh copy (just be sure to back up your work first if you do that).