This fixes the insecure content errors/warning on the example page.

Assets aren't loading in Chrome browser because of an insecure content warning.

The page at 'https://fkchang.github.io/opal-irb/index-jq.html' was loaded over HTTPS, but ran insecure content from 'http://codemirror.net/keymap/emacs.js': this content should also be loaded over HTTPS.