Bump serialize-javascript and terser-webpack-plugin in /assets

Bumps [serialize-javascript](https://github.com/yahoo/serialize-javascript) to 6.0.2 and updates ancestor dependency [terser-webpack-plugin](https://github.com/webpack-contrib/terser-webpack-plugin). These dependencies need to be updated together.


Updates `serialize-javascript` from 6.0.0 to 6.0.2
- [Release notes](https://github.com/yahoo/serialize-javascript/releases)
- [Commits](yahoo/serialize-javascript@v6.0.0...v6.0.2)

Updates `terser-webpack-plugin` from 2.3.8 to 5.3.11
- [Release notes](https://github.com/webpack-contrib/terser-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/terser-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/terser-webpack-plugin@v2.3.8...v5.3.11)

---
updated-dependencies:
- dependency-name: serialize-javascript
  dependency-type: indirect
- dependency-name: terser-webpack-plugin
  dependency-type: direct:development
...

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