Use Gitter Icon with Link

[rprouse]

I just check Font Awesome 5 including Pro and they still don't have a Gitter icon. There is an SVG Gitter icon available on https://simpleicons.org/ though, we could probably use that.

[rprouse]

Font Awesome 5 has been released and the free icons include a Gitter icon. If we upgrade, we could use that.