Bump y18n from 4.0.0 to 4.0.3 in /demo (#22)

Bumps [y18n](https://github.com/yargs/y18n) from 4.0.0 to 4.0.3.
- [Release notes](https://github.com/yargs/y18n/releases)
- [Changelog](https://github.com/yargs/y18n/blob/y18n-v4.0.3/CHANGELOG.md)
- [Commits](yargs/y18n@v4.0.0...y18n-v4.0.3)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>