Bump terser from 4.8.0 to 4.8.1 in /demo

Bumps [terser](https://github.com/terser/terser) from 4.8.0 to 4.8.1.
- [Release notes](https://github.com/terser/terser/releases)
- [Changelog](https://github.com/terser/terser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/terser/terser/commits)

---
updated-dependencies:
- dependency-name: terser
  dependency-type: indirect
...

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Author: dependabot[bot]