Bump showdown from 1.9.1 to 2.0.0

Bumps [showdown](https://github.com/showdownjs/showdown) from 1.9.1 to 2.0.0.
- [Release notes](https://github.com/showdownjs/showdown/releases)
- [Changelog](https://github.com/showdownjs/showdown/blob/2.0.0/CHANGELOG.md)
- [Commits](https://github.com/showdownjs/showdown/compare/1.9.1...2.0.0)

---
updated-dependencies:
- dependency-name: showdown
  dependency-type: direct:development
  update-type: version-update:semver-major
...
Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -83,7 +83,7 @@
     "sass": "^1.23.0",
     "scroll-into-view": "^1.8.2",
     "shallowequal": "^1.1.0",
-    "showdown": "^1.6.4",
+    "showdown": "^2.0.0",
     "sinon": "^13.0.0",
     "tailwindcss": "^3.0.2",
     "tiny-emitter": "^2.0.2",