Bump cssnano from 5.0.3 to 5.0.4 (#2067)

Bumps [cssnano](https://github.com/cssnano/cssnano) from 5.0.3 to 5.0.4.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@5.0.3...cssnano@5.0.4)

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