Include 'Ubuntu' font (used as system-ui in Chrome)

[lpellis]

The font-family: system-ui font is supposed to default to 'Ubuntu' on linux systems [1], currently it is defaulting to Verdana which is a much wider font, and is breaking the layout of some sites I'm testing.

I think it might be solved by simply including the correct font (Ubuntu) on the box. Or maybe depending on the distribution it can be set some other way?

[1] https://fontsarena.com/blog/operating-systems-default-sans-serif-fonts/

[joelgriffith]

Fixed in #617, should be out on hosted service in a few days!