Bukkit

• Added support for 1.16.2

Since 1.13, the policy for OpenInv is to support 1.8 and the latest 2 major versions. Since there hasn't been a minor version bump since Spigot took over from CraftBukkit, this hasn't been a concern before, but I now also intend to leave the latest 2 minor versions exclusively for the current major version to ease upgrades for server owners. Older major versions will always only support the last released minor version.