Bump http-proxy-middleware and laravel-mix

Bumps [http-proxy-middleware](https://github.com/chimurai/http-proxy-middleware) to 2.0.7 and updates ancestor dependency [laravel-mix](https://github.com/JeffreyWay/laravel-mix). These dependencies need to be updated together.


Updates `http-proxy-middleware` from 0.19.1 to 2.0.7
- [Release notes](https://github.com/chimurai/http-proxy-middleware/releases)
- [Changelog](https://github.com/chimurai/http-proxy-middleware/blob/v2.0.7/CHANGELOG.md)
- [Commits](chimurai/http-proxy-middleware@v0.19.1...v2.0.7)

Updates `laravel-mix` from 4.1.4 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: http-proxy-middleware
  dependency-type: indirect
- dependency-name: laravel-mix
  dependency-type: direct:development
...

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