Fix a typo leading to `paginate(plt; row, col)` failures

[lcontento]

~~I have a plot with many facets that I am not able to paginate using the col and row arguments.~~ paginate(plt; row, col) called on a plot that has no row/col inside mapping throws an error. Fixing this typo prevents the error.

[lcontento]

After double-checking, while this solves the error that paginate raised, it does not fix my actual problem... I will look a bit more into this and update this PR. If I can't get to the bottom of it, then I'll close the PR and open an issue.

[lcontento]

In the end, I did not read with enough attention the docstring and did not notice that you need to specify row and col in mapping too... Still, I think paginate(plt; row, col) should not throw never throw an error, so fixing this typo is not completely useless even if not particularly useful.