chore: bump rxjs from 6.6.3 to 7.8.1

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.6.3 to 7.8.1.
- [Changelog](https://github.com/ReactiveX/rxjs/blob/7.8.1/CHANGELOG.md)
- [Commits](ReactiveX/rxjs@6.6.3...7.8.1)

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

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

package.json

@@ -31,7 +31,7 @@
     "homepage": "https://github.com/Colonise/DataSource#readme",
     "devDependencies": {
         "@colonise/config": "^3.17.0",
-        "rxjs": "^6.6.3"
+        "rxjs": "^7.8.1"
     },
     "dependencies": {
         "@colonise/utilities": "^6.3.2",