Bump reveal.js from 3.9.2 to 4.3.1

Bumps [reveal.js](https://github.com/hakimel/reveal.js) from 3.9.2 to 4.3.1.
- [Release notes](https://github.com/hakimel/reveal.js/releases)
- [Commits](hakimel/reveal.js@3.9.2...4.3.1)

---
updated-dependencies:
- dependency-name: reveal.js
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -38,7 +38,7 @@
  "jquery": "^3.1.0",
  "load-awesome": "^1.1.0",
  "lodash": "4.17.19",
- "reveal.js": "^3.3.0",
+ "reveal.js": "^4.3.1",
  "selectize": "^0.12.2",
  "selectize-scss": "^0.9.1",
  "simple-masonry": "1.0.5",