Pagination border is cut off on hover

Created by: sqal

This bug is present in the lastest stable version (4.0)

Steps to reproduce

• Go to https://getbootstrap.com/docs/4.0/components/pagination/
• Using chrome devtools force .page-link to be in hover state
• Change border color to e..g red to see the bug

Looks like z-index for :hover was accidentally removed in this commit https://github.com/twbs/bootstrap/commit/797149ed267c59189fcf043c1a95484cfb9c7469