Bump socket.io from 2.3.0 to 2.4.0

Bumps [socket.io](https://github.com/socketio/socket.io) from 2.3.0 to 2.4.0.
- [Release notes](https://github.com/socketio/socket.io/releases)
- [Changelog](https://github.com/socketio/socket.io/blob/2.4.0/CHANGELOG.md)
- [Commits](socketio/socket.io@2.3.0...2.4.0)

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

Author: dependabot[bot]

package-lock.json

@@ -45,7 +45,7 @@
     "passport-local": "^1.0.0",
     "path": "^0.12.7",
     "sequelize": "^4.44.4",
-    "socket.io": "^2.3.0",
+    "socket.io": "^2.4.0",
     "timer.js": "^1.0.4"
   },
   "devDependencies": {