Bump rxjs from 7.2.0 to 7.4.0 in /app

Bumps [rxjs](https://github.com/reactivex/rxjs) from 7.2.0 to 7.4.0.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/reactivex/rxjs/compare/7.2.0...7.4.0)

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

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

app/package.json

@@ -29,7 +29,7 @@
     "mz": "^2.7.0",
     "native-process-working-directory": "^1.0.2",
     "npm": "6",
-    "rxjs": "^7.2.0",
+    "rxjs": "^7.4.0",
     "source-map-support": "^0.5.20",
     "v8-compile-cache": "^2.3.0",
     "yargs": "^17.1.0"