Use the latest highlight.js version

[anarthal]

The currently used version is old and doesn't seem to parse C++ very well:

Newer versions seem to work better:

(Run with the official demo, which at the time of writing should be using 11.9.0).

[rbbeeston]

We should see if it's an issue inherent to highlight.js, even in the newer versions. We would be open to recommendations of a better highlighter.

[alandefreitas]

The code blocks in the reference also contain links, etc... They're not verbatim. This might be related to the issue.

[sdarwin]

we should try upgrading all packages to the latest versions, not only highlight.js

[julioest]

@sdarwin #401