build(deps-dev): bump memdown from 5.1.0 to 6.0.0

Bumps [memdown](https://github.com/Level/memdown) from 5.1.0 to 6.0.0.
- [Release notes](https://github.com/Level/memdown/releases)
- [Changelog](https://github.com/Level/memdown/blob/master/CHANGELOG.md)
- [Commits](Level/memdown@v5.1.0...v6.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -104,7 +104,7 @@
     "jest-canvas-mock": "~2.3.0",
     "jest-environment-jsdom-sixteen": "~1.0.3",
     "lint-staged": "~10.5.0",
-    "memdown": "~5.1.0",
+    "memdown": "~6.0.0",
     "prettier": "~2.2.0",
     "react-select-event": "~5.3.0",
     "react-test-renderer": "~17.0.1",