CSS Enhancement - Add support for `flow-root` as value for `display` property

[praveenpuglia]

display: flow-root is now a thing and I thought it would be nice to have it come up on autocompletion.

I am coming here from here.

Raised a PR #13334 . Please let me know if I missed something.
Ref -

• http://caniuse.com/#feat=flow-root
• https://developer.mozilla.org/en-US/docs/Web/CSS/display

[petetnt]

Fixed in #13334! 👍