Styles not being applied when component is inside a collapsible element

Hi, great lib! It is helping me very much.

I notice that, when the `` or `` is placed inside a collapsible element which in the first render has a `display: none;`, it doesn't render correctly.

[Here is the reproduced example in codesandbox](https://codesandbox.io/s/react-nice-dates-bug-collapse-mno8d?file=/src/Example.js:427-437)

Going further, [comparing](https://www.diffchecker.com/PuDLODta) with the rendered element in the docs, I see that the `wide` class is not applied to `.nice-dates-day` and `.nice-dates-grid` is rendered with `height: 6px`.

Perhaps this happens because the initial width of the `ref` element is 0 and by that it can't render correctly?

I can open a PR setting a mininum height for `.nice-dates-day` and `.nice-dates-grid` but I'd like to discuss it here before to check if this is the best option available.