Bump engine.io and socket.io in /frontend

Bumps [engine.io](https://github.com/socketio/engine.io) to 3.6.1 and updates ancestor dependency [socket.io](https://github.com/socketio/socket.io). These dependencies need to be updated together.


Updates `engine.io` from 3.4.0 to 3.6.1
- [Release notes](https://github.com/socketio/engine.io/releases)
- [Changelog](https://github.com/socketio/engine.io/blob/main/CHANGELOG.md)
- [Commits](socketio/engine.io@3.4.0...3.6.1)

Updates `socket.io` from 2.3.0 to 2.5.0
- [Release notes](https://github.com/socketio/socket.io/releases)
- [Changelog](https://github.com/socketio/socket.io/blob/main/CHANGELOG.md)
- [Commits](socketio/socket.io@2.3.0...2.5.0)

---
updated-dependencies:
- dependency-name: engine.io
  dependency-type: indirect
- dependency-name: socket.io
  dependency-type: direct:production
...

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

Author: dependabot[bot]

frontend/package-lock.json

@@ -11,7 +11,7 @@
     "axios": "^0.19.0",
     "core-js": "^2.6.5",
     "iview": "^3.4.2",
-    "socket.io": "^2.3.0",
+    "socket.io": "^2.5.0",
     "socket.io-client": "^2.3.0",
     "vue": "^2.6.10",
     "vuex": "^3.1.1"