Updating all kata to use Lean v3.20.c

Stream: Codewars

[Donald Sebastian Leung]

May I kindly ask all kata authors to update their content to Lean v3.20.c if they haven't done so already? This way, we will be able to request for an updated Lean version on schedule by the beginning of December which is crucial to ensure the continued quality of our platform as a resource to practice on Lean considering how fast things are evolving with Lean and mathlib. Thanks!

The full list of Kata to update can be found here, which has been reduced from 21 kata down to 10 over the past month: https://github.com/codewars/codewars.com/wiki/List-of-Lean-Kata-to-Update