build(deps): bump postcss-selector-parser in /docs

Bumps  and [postcss-selector-parser](https://github.com/postcss/postcss-selector-parser). These dependencies needed to be updated together.

Updates `postcss-selector-parser` from 6.1.4 to 6.1.5
- [Release notes](https://github.com/postcss/postcss-selector-parser/releases)
- [Changelog](https://github.com/postcss/postcss-selector-parser/blob/6.1.5/CHANGELOG.md)
- [Commits](postcss/postcss-selector-parser@6.1.4...6.1.5)

Updates `postcss-selector-parser` from 7.1.5 to 7.1.7
- [Release notes](https://github.com/postcss/postcss-selector-parser/releases)
- [Changelog](https://github.com/postcss/postcss-selector-parser/blob/6.1.5/CHANGELOG.md)
- [Commits](postcss/postcss-selector-parser@6.1.4...6.1.5)

---
updated-dependencies:
- dependency-name: postcss-selector-parser
  dependency-version: 6.1.5
  dependency-type: indirect
- dependency-name: postcss-selector-parser
  dependency-version: 7.1.7
  dependency-type: indirect
...

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Author: dependabot[bot]