Change product iteration order

Trivial, but seems more consistent to me. Changes `product(1:2, 1:2)` from
`[(1,1), (2,1), (1, 2), (2, 2)]` to
`[(1,1), (1,2), (2, 1), (2, 2)]`, which is consistent with `permutations` (and sorting or cross joining DataFrames).