Bump cross-spawn from 6.0.5 to 6.0.6 in /backend

Bumps [cross-spawn](https://github.com/moxystudio/node-cross-spawn) from 6.0.5 to 6.0.6.
- [Changelog](https://github.com/moxystudio/node-cross-spawn/blob/v6.0.6/CHANGELOG.md)
- [Commits](moxystudio/node-cross-spawn@v6.0.5...v6.0.6)

---
updated-dependencies:
- dependency-name: cross-spawn
  dependency-type: indirect
...

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Author: dependabot[bot]