nukkit jar file is not included. you have to download the latest version yourself: https://ci.nukkitx.com/job/NukkitX/job/Nukkit/job/master/

It is possible if you download this file in the future, that the plugins are outdated. You have to just replace the jars, that's all.

Downloads:

DBLIB: https://nukkitx.com/resources/dblib.12/

FAWE NK: https://nukkitx.com/resources/fastasyncworldedit.30/

PlotSquared NK: https://nukkitx.com/resources/plotsquared.31/