Modal overlay is not scrollable

[vagrantsn]

The modal overlay doesn't allow scrolling for modals that doesn't fit the screen. We need to add an overflow rule to the .overlay class:

https://github.com/pagarme/former-kit-skin-pagarme/blob/7fb9e756674ab85eeb88485dfce341c214c2642a/src/styles/modal/index.css#L31

This issue affects all modals and Pull Request Pilot/928