It is updated, just make you have the latest BiomeGenerator and PlotSquared. You're doing nothing wrong, but something that helps is using another world as the base. If you have a vanilla world, set that in the config.yml The nether terrain isn't attributed to the biome, but rather the world type (overworld, nether, end). This also applies to sky. And a few other biomes like ice plains don't work for other reasons.