Bump color-string from 1.5.3 to 1.9.0 in /docs (#27)

Bumps [color-string](https://github.com/Qix-/color-string) from 1.5.3 to 1.9.0.
- [Release notes](https://github.com/Qix-/color-string/releases)
- [Changelog](https://github.com/Qix-/color-string/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Qix-/color-string/commits/1.9.0)

---
updated-dependencies:
- dependency-name: color-string
  dependency-type: indirect
...

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