Replace broken link in LeaveOneOutEncoder docs

[PaulWestenthanner]

Expected Behavior

Working link to further readings on how the leave-on-out-encoder works

Actual Behavior

404 Error on kaggle page. It seems that the whole competition was removed.

Steps to Reproduce the Problem

Klick link.

Solutions

Use either
https://pkghosh.wordpress.com/2018/06/18/leave-one-out-encoding-for-categorical-feature-variables-on-spark/
or
https://datascience.stackexchange.com/questions/10839/what-is-difference-between-one-hot-encoding-and-leave-one-out-encoding

Unfortunately a paper cannot be found.