Rails already creates little pre-gzipped `.gz` copies of all our assets
in the `public/assets` directory when we build. This configures nginx to
send those when available!
We weren't doing *any* gzip stuff before, so this helps a lot with those
bigger JS files, like the `wardrobe-2020` stuff. It's now at ~.5MB with
compression, which is still a bit big, but nowhere near as offensive as
the 4.5MB pre-anything, or 1.5MB post-minification, lol.
