A test authorization for www.jonrowlison.com to the Let's Encrypt staging service has revealed issues that may prevent any certificate for this domain being issued.
Fetching http://www.jonrowlison.com/.well-known/acme-challenge/d2nNHd_4KhTtrMatVhAY4ue87n0MOyvhQ_gWsi9tEmc: Timeout during connect (likely firewall problem)