fix(coordinateGridMixin): renderVerticalGridLines should consider useTopXAxis

[aberenyi]

Fixes #1818

[aberenyi]

@gordonwoodhull would you mind to review this whenever you have a spare few mins?

[gordonwoodhull]

Sorry for the slow response. This makes sense to me and I will merge it next release.

If you would be so kind as to add a test case or two, we can ensure that the new feature keeps working into the future.

If you add a test case that fails without this fix and succeeds with it, I think that will be sufficient to test useTopXAxis. It wouldn't hurt to also test something from the last PR #1816, like _xAxisY() or the translate on the label position.

Thanks!

[aberenyi]

@gordonwoodhull no probs at all.

Will try to write some tests in due course.

Cheers