Bump electron from 9.0.3 to 9.4.0 in /demos

Bumps [electron](https://github.com/electron/electron) from 9.0.3 to 9.4.0.
- [Release notes](https://github.com/electron/electron/releases)
- [Changelog](https://github.com/electron/electron/blob/master/docs/breaking-changes.md)
- [Commits](electron/electron@v9.0.3...v9.4.0)

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Author: dependabot[bot]