Bump socket.io from 1.3.7 to 2.5.0

Bumps [socket.io](https://github.com/socketio/socket.io) from 1.3.7 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@1.3.7...2.5.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -25,7 +25,7 @@
     "underscore": "~1.8.3",
     "express": "~4.13.3",
     "mustache": "~2.1.3",
-    "socket.io": "~1.3.7"
+    "socket.io": "~2.5.0"
   },
   "devDependencies": {
     "grunt-contrib-qunit": "~0.7.0",