Bump ajv and react-scripts-ts

Bumps [ajv](https://github.com/ajv-validator/ajv) to 6.12.6 and updates ancestor dependency [react-scripts-ts](https://github.com/wmonk/create-react-app). 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 `react-scripts-ts` from 3.1.0 to 4.0.8
- [Changelog](https://github.com/wmonk/create-react-app/blob/next/CHANGELOG.md)
- [Commits](https://github.com/wmonk/create-react-app/commits)

---
updated-dependencies:
- dependency-name: ajv
  dependency-type: indirect
- dependency-name: react-scripts-ts
  dependency-type: direct:development
...

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

Author: dependabot[bot]