The short-lived max-age value set previously was overridden by the
higher value of 1800 (30 mins) set in CloudFlare's "Browser Cache TTL"
setting under Page Rules for cdn.hypothes.is.

Resolve this by simply disabling caching of the entry point for qa
deployments. This means that https://cdn.hypothes.is/hypothesis@qa will
always return the boot script for the latest client QA release.