melonDS on Flathub license is (slightly) wrong.

[cameronbosch]

Hi. I was browsing Flathub, and I saw that the license for melonDS was incorrectly marked as GPLv3 only, when it should be marked (according to this very repository) as GPLv3 or later.

melonDS is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

It's not urgent, but maybe this should be fixed on the Flathub manifest file on Flathub (given this is a verified by the official team) for the official Flatpak app?