Fix Prettify Link

[tajmone]

Fix Prettify Syntax Highlighter Link

The link to prettify highlight in §46.2. Available Source Highlighters is obsolete, prettify has now officially moved to GitHub.

Old link:

• https://code.google.com/archive/p/google-code-prettify/

New link:

• https://github.com/google/code-prettify

[tajmone]

Please, delete branch after merging in!

[mojavelinux]

Thanks for the update!