Bump reveal.js from 3.9.2 to 4.2.1

[dependabot]

Bumps reveal.js from 3.9.2 to 4.2.1.

Release notes

Sourced from reveal.js's releases.

4.2.1

Bug fix release 🐛

Fixes

• Fix an issue where some slides disappeared (fully or partially) after slide transitions in Chrome (9e583b8df4edecb94cb89f012ae5c80014a859ee @​hakimel)
• Fix an issue that caused double-navigations and impacted presentation performance (@​hakimel #3079)
• Fix --host not working in npm start -- --host=0.0.0.0 (@​cashcat #3075)
• Fix incorrect sizing of auto-sized text in PDF exports (hakimel/reveal.js#2865 @​hakimel)
• Fix background video playback issue in some browsers by inferring MIME type from file extension (#3078 @​vanch3d)

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;
</tr></table> 

... (truncated)

Commits

• c804611 dark mode logo
• 79a1674 4.2.1
• 9e583b8 fix intermittent issue with partially disappearing slides in scaled down pres...
• 74c0fbb fix read issue that caused double navigations fixes #3079
• c5d5498 refactor #3078
• ec32d44 remove comment
• bded1f5 Merge pull request #3078 from vanch3d/video
• 2d050a8 Merge pull request #3075 from cashcat/patch1
• 907ec73 rebuilt dist files (reveal.js only)
• bcf8315 adding type to the video source tag
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot close will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

[dependabot]

Superseded by #340.