stability index wrapping

[Trott]

• URL: https://nodejs.org/dist/latest-v8.x/docs/api/documentation.html
• Browser version: Chrome 60.0.3112.90 (Official Build) (64-bit)
• Operating system: macOS 10.12.6

The stability index text banners do not wrap, requiring lots of scrolling right to read the text.

[saadq]

It looks like the styles for the docs and the api stability stuff was in the main node repo, so I opened a PR that should fix this over there. Is that alright?