[cashtab] enable gzip compression when serving cashtab
local testing showed a notable improvement on load time.
docker build -t cashtab_local . docker run --rm -p 8080:80 --name cashtab cashtab_local
send and receive tokens and BCH. also the generated Lighthouse report on localhost:8080 in an incognito window shows a ~60% reduced Time to Interactive metric over master.
Reviewers: #bitcoin_abc, josephroyking
Reviewed By: #bitcoin_abc, josephroyking
Differential Revision: https://reviews.bitcoinabc.org/D9472