Update to Extending doc breaks docs site build

[verythorough]

- Do you want to request a feature or report a bug?
docs bug

- What is the current behavior?
While preparing to preview a docs edit, I discovered that builds on the netlify-cms-www repo have been failing since 64b0d4c. This is because the site is built with Hugo, and it's trying to process the shortcode syntax that's now in the code sample.

- If the current behavior is a bug, please provide the steps to reproduce.
Go to https://www.netlifycms.org/docs/extending/ and see that the new version has not published.

- What is the expected behavior?
Content on https://www.netlifycms.org/docs should match content in https://github.com/netlify/netlify-cms/tree/master/docs.

I discovered that you can escape the shortcodes by adding /* */ inside them, and it works in the Hugo-built site:

However, the version on GitHub still shows the escape characters:

Ah, the joys of writing markdown for two simultaneous interpreters!

[erquhart]

Great catch @verythorough, reverted in 83a1d34.