doc(tactic/cache): fix haveI docs (#8637)
doc(tactic/cache): fix haveI docs (#8637)

Applies [Bhavik's suggestion](https://github.com/leanprover-community/mathlib/pull/8631#discussion_r687260852) which missed the train for #8631.



leanprover-community/mathlib,leanprover-community/mathlib