Handle Astro syntax highlighting correctly

[simonplend]

I plan to raise an issue on the Astro repo asking if they'd welcome a PR that exposes plugin.js from the @astrojs/prism package.

If they're open to it, this would fix the hack introduced in #19.

[HassanBahati]

@mcollina could this issue have been addressed in #19 . Perhaps we could have it closed if completed.

[simonplend]

Unfortunately this issue is not resolved by PR #19 - it was actually created in relation to fixing a hack introduced by that PR:

If they're open to it, this would fix the hack introduced in #19.

Re-opening this issue.