Bump ajv and har-validator

Bumps [ajv](https://github.com/ajv-validator/ajv) and [har-validator](https://github.com/ahmadnassri/node-har-validator). These dependencies needed 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 `har-validator` from 5.1.0 to 5.1.5
- [Release notes](https://github.com/ahmadnassri/node-har-validator/releases)
- [Changelog](https://github.com/ahmadnassri/node-har-validator/blob/master/.releaserc)
- [Commits](ahmadnassri/node-har-validator@v5.1.0...v5.1.5)

---
updated-dependencies:
- dependency-name: ajv
  dependency-type: indirect
- dependency-name: har-validator
  dependency-type: indirect
...

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