Bump ajv from 6.12.2 to 6.12.6 in /addons/gst-web/src (#118)

Bumps [ajv](https://github.com/ajv-validator/ajv) from 6.12.2 to 6.12.6.
- [Release notes](https://github.com/ajv-validator/ajv/releases)
- [Commits](ajv-validator/ajv@v6.12.2...v6.12.6)

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

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