Bump webpack-dev-server from 4.7.4 to 4.8.1 (#483)

Bump webpack-dev-server from 4.7.4 to 4.8.1 (#483)

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 4.7.4 to 4.8.1.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack/webpack-dev-server/compare/v4.7.4...v4.8.1)

---
updated-dependencies:
- dependency-name: webpack-dev-server
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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