Bump rxjs from 6.6.2 to 7.8.1

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.6.2 to 7.8.1.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/7.8.1/CHANGELOG.md)
- [Commits](ReactiveX/rxjs@6.6.2...7.8.1)

---
updated-dependencies:
- dependency-name: rxjs
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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