Bump engine.io and karma

Bumps [engine.io](https://github.com/socketio/engine.io) to 6.2.1 and updates ancestor dependency [karma](https://github.com/karma-runner/karma). These dependencies need to be updated together.


Updates `engine.io` from 3.1.5 to 6.2.1
- [Release notes](https://github.com/socketio/engine.io/releases)
- [Changelog](https://github.com/socketio/engine.io/blob/main/CHANGELOG.md)
- [Commits](https://github.com/socketio/engine.io/compare/3.1.5...6.2.1)

Updates `karma` from 2.0.0 to 6.4.1
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](https://github.com/karma-runner/karma/compare/v2.0.0...v6.4.1)

---
updated-dependencies:
- dependency-name: engine.io
  dependency-type: indirect
- dependency-name: karma
  dependency-type: direct:development
...

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

package.json

@@ -40,7 +40,7 @@
     "chai": "^4.1.2",
     "concat": "azer/concat",
     "concat-cli": "^4.0.0",
-    "karma": "^2.0.0",
+    "karma": "^6.4.1",
     "karma-chai": "^0.1.0",
     "karma-firefox-launcher": "^1.1.0",
     "karma-mocha": "^1.3.0",