staging-pulls has invalid https cert

[lukebjerring]

See https://pulls-staging.web-platform-tests.org

Note that the site is also using HSTS, so completely unavailable.

[lukebjerring]

Seems we should automatically update the cert using certbot
https://certbot.eff.org/#ubuntuother-nginx

Found this example which sets it up using ansible
https://gist.github.com/evantahler/1b241958b9ea175c68924948e5a52743