fix hardcoded path in .arclint
fix hardcoded path in .arclint

A long while ago we migrated to preferring using `$PATH` and not
assuming hardcoded tool locations on the system.  Looks like we missed
that in this repository.

(Kinda ironic, since this is the repo for the linter itself)

Test plan: run `arc lint`

Khan/khan-linter,Khan/khan-linter,Khan/khan-linter,Khan/khan-linter