Bump js-yaml from 4.1.1 to 4.2.0 in /common/webapp (#811)

Bumps [js-yaml](https://github.com/nodeca/js-yaml) from 4.1.1 to 4.2.0.
- [Changelog](https://github.com/nodeca/js-yaml/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nodeca/js-yaml/commits)

---
updated-dependencies:
- dependency-name: js-yaml
  dependency-version: 4.2.0
  dependency-type: indirect
...

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