Focus escapes modal when first or last element has style `display: none`

[pzhine]

Summary:

The 3.8.1 release of react-modal allows the focus to escape when the first or last tabbable element has style display: none

Steps to reproduce:

1. Open a react-modal with a few tabbable elements where the first or last tabbable element style set to display: none.
2. Press tab or shift-tab a few times.
3. When it gets to the first/last tabbable item, the tab or shift-tab event moves the focus outside the modal.

Expected behavior:

The tab and shift-tab events never move the focus outside the modal

Link to example of issue:

https://codesandbox.io/s/4x2nlqq599

[flurmbo]

Hi @diasbruno, is it okay if I give a go at this issue?

[diasbruno]

Sure, @flurmbo. Contributions are always welcome. Let me know if you need anything.