Bump elliptic from 6.4.0 to 6.5.3 in /demo

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.4.0 to 6.5.3.
- [Release notes](https://github.com/indutny/elliptic/releases)
- [Commits](indutny/elliptic@v6.4.0...v6.5.3)

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

Author: dependabot[bot]