enhance(Makefile): double-quote if check
enhance(Makefile): double-quote if check

Co-authored-by: Lars Yencken <3318dc5ce3e4fb7c28a0b841b6801c884e1d0896@yencken.org>
owid/owid-grapher,owid/owid-grapher,owid/owid-grapher,owid/owid-grapher,owid/owid-grapher