chore(deps): bump serialize-javascript in /playground/www

Bumps [serialize-javascript](https://github.com/yahoo/serialize-javascript) from 2.1.2 to 6.0.0.
- [Release notes](https://github.com/yahoo/serialize-javascript/releases)
- [Commits](yahoo/serialize-javascript@v2.1.2...v6.0.0)

---
updated-dependencies:
- dependency-name: serialize-javascript
  dependency-type: indirect
...

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