Bump postcss-loader from 7.0.2 to 7.1.0

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.0.2 to 7.1.0.
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](webpack/postcss-loader@v7.0.2...v7.1.0)

---
updated-dependencies:
- dependency-name: postcss-loader
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]