Question [GPL] Using Bukkit 1.7 code in another application

I'm currently developing a game that will be released under GPLv3-or-later, and I've been wondering whether I could use Bukkit's org.bukkit.util.noise package in it. Bukkit is released under the terms of GNU General Public License version 3, so I do have the permission to reuse code so long as I give credit and I license my work under GPLv3. However, nowhere does it say whether Bukkit is licensed under GPLv3-only or GPLv3-or-later. This matters because I cannot release GPLv3-only code under GPLv3-or-later terms. This is usually specified in the copyright notice present in every source file but there is no such notice, only LICENCE.txt (which for obvious reasons does not provide this information). Does anyone know which case is it? Is Bukkit (not CraftBukkit) released under the terms of GPLv3-only or GPLv3-or-later?