Bump ajv and rewire

Bumps [ajv](https://github.com/ajv-validator/ajv) to 6.12.6 and updates ancestor dependency [rewire](https://github.com/jhnns/rewire). These dependencies need to be updated together.


Updates `ajv` from 5.5.2 to 6.12.6
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v5.5.2...v6.12.6)

Updates `rewire` from 4.0.1 to 6.0.0
- [Release notes](https://github.com/jhnns/rewire/releases)
- [Changelog](https://github.com/jhnns/rewire/blob/master/CHANGELOG.md)
- [Commits](jhnns/rewire@v4.0.1...v6.0.0)

---
updated-dependencies:
- dependency-name: ajv
  dependency-type: indirect
- dependency-name: rewire
  dependency-type: direct:development
...

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

Author: dependabot[bot]