chore(deps): bump rxjs from 6.6.6 to 6.6.7 in /frontend

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.6.6 to 6.6.7.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/6.6.7/CHANGELOG.md)
- [Commits](ReactiveX/rxjs@6.6.6...6.6.7)

Signed-off-by: dependabot[bot] <support@github.com>