Bump braces and webpack-cli in /assets

Removes [braces](https://github.com/micromatch/braces). It's no longer used after updating ancestor dependency [webpack-cli](https://github.com/webpack/webpack-cli). These dependencies need to be updated together.


Removes `braces`

Updates `webpack-cli` from 3.3.12 to 5.1.4
- [Release notes](https://github.com/webpack/webpack-cli/releases)
- [Changelog](https://github.com/webpack/webpack-cli/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack/webpack-cli/compare/[email protected])

---
updated-dependencies:
- dependency-name: braces
  dependency-type: indirect
- dependency-name: webpack-cli
  dependency-type: direct:development
...

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