Bump elliptic and @cityofzion/neon-core (#471)

Bumps [elliptic](https://github.com/indutny/elliptic) to 6.6.1 and updates ancestor dependency [@cityofzion/neon-core](https://github.com/CityOfZion/neon-js). These dependencies need to be updated together.


Updates `elliptic` from 6.5.4 to 6.6.1
- [Commits](indutny/elliptic@v6.5.4...v6.6.1)

Updates `@cityofzion/neon-core` from 5.0.0-next.12 to 5.7.0
- [Release notes](https://github.com/CityOfZion/neon-js/releases)
- [Commits](https://github.com/CityOfZion/neon-js/commits)

---
updated-dependencies:
- dependency-name: elliptic
  dependency-type: indirect
- dependency-name: "@cityofzion/neon-core"
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>