Minor fix suggested in Recommenders repo

[AbhiramE]

Update floor division to division based on the comment received in Recommenders repo.

no, using math is fine, but the // operator does integer division which will round down (10 // 3 = 3), so the ceil is not actually doing anything. but if you do (10 / 3 = 3.333) then apply ceil you will get 4 which is what I'm assuming you want.

recommenders-team/recommenders#813 (comment)