Bump ssri from 6.0.1 to 6.0.2 in /demo (#15)

Bumps [ssri](https://github.com/npm/ssri) from 6.0.1 to 6.0.2.
- [Release notes](https://github.com/npm/ssri/releases)
- [Changelog](https://github.com/npm/ssri/blob/v6.0.2/CHANGELOG.md)
- [Commits](npm/ssri@v6.0.1...v6.0.2)

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