Bump reveal.js from 3.9.2 to 4.2.0

[dependabot]

Bumps reveal.js from 3.9.2 to 4.2.0.

Release notes

Sourced from reveal.js's releases.

4.2.0

Changes

• The math plugin now supports three typesetting libraries: KaTeX, MathJax 2 and MathJax 3. We continue to use MathJax 2 as our default so this is fully backwards compatible. Learn how to choose between typesetters and how to configure them in the docs at https://revealjs.com/math#typesetting-libraries (@​burgerga in #2559).
• New event: beforeslidechange (#3003). This makes it possible to conditionally prevent navigations:

  // This prevents all slide changes
  Reveal.addEventListener( 'beforeslidechange', e => e.preventDefault() );

• New keyboard shortcut for skipping fragments while navigating: alt + ←/↑/→/↓.
• New API option for skipping fragments in directional navigation Reveal.right({ skipFragments: true }).
• Adds a beforeHighlight callback to the highlight plugin (@​rajgoel in #3026).

  Reveal.initialize({ 
    highlight: {
      beforeHighlight: (hljs) => {
        // interact with highlight.js, for example to register a new language
      }
    } 
  })

• Code line numbers can now start from an offset (#3050). For example, this code block would begin its line numbering from 10: <code data-ln-start-from="10">.
• Better error messaging when the .reveal or .slides containers are missing #2217.

Fixes

• The last slide keyboard shortcut now works for looped presentations (#3007).
• Markdown code blocks can be turned into fragments (@​nicojs in #2982).
• Unit tests can now run in Windows (@​Vandivier in #3027).
• Restored support for base64 background images, broken since 4.1.1 (#2978).
• Fixes an issue that prevented presentations from looping when navigationMode was set to linear.
• Internal links leading to a slide with video/audio element will now correctly start media playback. This issue only affected mobile browsers.

4.1.2

Changes

• Adds support for data-auto-animate-restart and data-auto-animate-id. These properties give you finer control over which slides that should auto-animate between each other (@​coffeenotfound in #2896).
• Theme properties are now available as CSS variables, making them easy to override. Full list of variables (#2740 + #2968). Here's an example you can drop into your presentation's HTML:

<style type="text/css">
:root {
  --r-background-color: indigo;
  --r-main-color: #f5f5f5;
  --r-main-font: monospace;
}
</style>

Fixes

• Markdown enabled speaker notes (<aside class="notes" data-markdown>) are no longer visible on-slide.

4.1.1

... (truncated)

Commits

• 6371351 4.2.0
• 2921e05 4.2.0
• 7f376c5 copy
• ceed5ed roll back unintended changes to default template
• 4e8a1b3 fix issue with internal links
• ad46e62 upgrade highlight.js line number plugin, adds support for line number offsets...
• bc94d95 roll back unintended change to build
• a6c0f3e refactor hash parsing, fixes issue with autoplaying media not starting from i...
• 35b67a9 katex math rendering; fix broken 2477 delimiter, compatibility with external ...
• 1ce77db tweak browser targets
• Additional commits viewable in compare view

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[dependabot]

Superseded by #331.