Bump body-parser from 2.3.0 to 2.4.0 in /demo (#2051)

Bumps [body-parser](https://github.com/expressjs/body-parser) from 2.3.0 to 2.4.0.
- [Release notes](https://github.com/expressjs/body-parser/releases)
- [Changelog](https://github.com/expressjs/body-parser/blob/master/HISTORY.md)
- [Commits](expressjs/body-parser@v2.3.0...v2.4.0)

---
updated-dependencies:
- dependency-name: body-parser
  dependency-version: 2.4.0
  dependency-type: indirect
...

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