Use new shortcode syntax

Since this page depends on brand new Hugo code, you might as well use the new syntax. {{< means no Markdown processing.

Oh, and if you want pull requests to this blog, I would put /public in .gitignore.

One more comment:

I really like this feature, but I see no big point in the index/url in frontmatter. Adding the urls/paths to the jsons directly in the function (GetJson(http://...) would  make it cleaner.