Bump ms, express and socket.io

Bumps [ms](https://github.com/vercel/ms) to 2.0.0 and updates ancestor dependencies [ms](https://github.com/vercel/ms), [express](https://github.com/expressjs/express) and [socket.io](https://github.com/socketio/socket.io). These dependencies need to be updated together.


Updates `ms` from 0.6.2 to 2.0.0
- [Release notes](https://github.com/vercel/ms/releases)
- [Commits](vercel/ms@0.6.2...2.0.0)

Updates `express` from 4.13.4 to 4.21.1
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.1/History.md)
- [Commits](expressjs/express@4.13.4...4.21.1)

Updates `socket.io` from 1.3.7 to 1.7.4
- [Release notes](https://github.com/socketio/socket.io/releases)
- [Changelog](https://github.com/socketio/socket.io/blob/1.7.4/History.md)
- [Commits](socketio/socket.io@1.3.7...1.7.4)

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

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

material/mi-pps-praesentation/plugin/multiplex/package.json

@@ -10,10 +10,10 @@
     "node": "~4.1.1"
   },
   "dependencies": {
-    "express": "~4.13.3",
+    "express": "~4.21.1",
     "grunt-cli": "~0.1.13",
     "mustache": "~2.2.1",
-    "socket.io": "~1.3.7"
+    "socket.io": "~1.7.4"
   },
   "license": "MIT"
 }