Improve speed of getTopUsers

[ajayyy]

This is using up a lot of CPU

[andrewzlee]

You indexing on userID?

[MRuy]

Until we have redis implemented i would implement a simple X minute in-memory cache

[Joe-Dowd]

Redis is already implemented (at least in the code): https://github.com/ajayyy/SponsorBlockServer/blob/master/src/utils/youtubeAPI.js

It's just waiting for ajay to put it on the server.