Bump elliptic from 6.5.6 to 6.6.1 in /examples/stable/demo/hello_world

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.5.6 to 6.6.1.
- [Commits](indutny/elliptic@v6.5.6...v6.6.1)

---
updated-dependencies:
- dependency-name: elliptic
  dependency-type: indirect
...

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