Support csszengarden.com over https

[frivoal]

I sometimes want to show the css zen garden HTML based presentations, so I put it in an iframe. But my slides are typically served over https, and embedding an http iframe in an https document is not allowed.

Serving the css zen garden over https in addition to http would be greatly appreciated.

Hopefully, this can easily (and cost free) be done with https://letsencrypt.org/.