Bump webpack-dev-middleware and laravel-mix

Bumps [webpack-dev-middleware](https://github.com/webpack/webpack-dev-middleware) to 5.3.4 and updates ancestor dependency [laravel-mix](https://github.com/JeffreyWay/laravel-mix). These dependencies need to be updated together.


Updates `webpack-dev-middleware` from 3.7.2 to 5.3.4
- [Release notes](https://github.com/webpack/webpack-dev-middleware/releases)
- [Changelog](https://github.com/webpack/webpack-dev-middleware/blob/v5.3.4/CHANGELOG.md)
- [Commits](webpack/webpack-dev-middleware@v3.7.2...v5.3.4)

Updates `laravel-mix` from 5.0.4 to 6.0.49
- [Release notes](https://github.com/JeffreyWay/laravel-mix/releases)
- [Changelog](https://github.com/laravel-mix/laravel-mix/blob/master/CHANGELOG.md)
- [Upgrade guide](https://github.com/laravel-mix/laravel-mix/blob/master/UPGRADE.md)
- [Commits](https://github.com/JeffreyWay/laravel-mix/commits)

---
updated-dependencies:
- dependency-name: webpack-dev-middleware
  dependency-type: indirect
- dependency-name: laravel-mix
  dependency-type: direct:development
...

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

Author: dependabot[bot]