Bump color-string and cssnano

Removes [color-string](https://github.com/Qix-/color-string). It's no longer used after updating ancestor dependency [cssnano](https://github.com/cssnano/cssnano). These dependencies need to be updated together.


Removes `color-string`

Updates `cssnano` from 3.10.0 to 5.1.14
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/[email protected])

---
updated-dependencies:
- dependency-name: color-string
  dependency-type: indirect
- dependency-name: cssnano
  dependency-type: direct:production
...

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