Simple Kelpies

- Updated to 1.20.1 (also works on 1.20)
- Kelpies now sink like skeleton horses when mounted. When not mounted, they will swim normally to maintain their disguise
(For some reason they do not move as fast as skeleton horses do underwater though, I plan to fix this later)
- Kelpies now get a super speed boost when wet. When it rains, you can get places crazy fast.