Bump rxjs from 6.5.3 to 6.5.4 in /app

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.5.3 to 6.5.4.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/6.5.4/CHANGELOG.md)
- [Commits](https://github.com/reactivex/rxjs/compare/6.5.3...6.5.4)

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

app/package.json

@@ -34,7 +34,7 @@
     "node-pty": "^0.10.0-beta2",
     "npm": "6.9.0",
     "path": "0.12.7",
-    "rxjs": "^6.5.3",
+    "rxjs": "^6.5.4",
     "rxjs-compat": "^6.5.4",
     "yargs": "^15.0.2",
     "zone.js": "^0.8.29"