Keep in mind that GOG does not patch the game, the developers do. GOG can ask nicely, but the fact is that they manage a large library of games and are less agile than you or I or the developers might be.
Of course, if GOG has the patch in their hands and hasn't yet pushed it through Galaxy/GOG.com, well that's another thing altogether.
Double Damage are most active on their Steam forum, and you can inquire there:
http://steamcommunity.com/app/290300/discussions/
Keep in mind two things of course: the developers have steadily and faithfully kept the GOG version updated, even if it lags behind the Steam updates, and that Steam players are a much larger market, so they're going to have the priority. This isn't laziness, it's two nice dudes making a game and updating it in only its second week of release.