Bump superdesk-planning from 3f640b1 to 8794d37 in /client (#492)

Bumps [superdesk-planning](https://github.com/superdesk/superdesk-planning) from `3f640b1` to `8794d37`.
- [Release notes](https://github.com/superdesk/superdesk-planning/releases)
- [Commits](superdesk/superdesk-planning@3f640b1...8794d37)

---
updated-dependencies:
- dependency-name: superdesk-planning
  dependency-type: direct:production
...

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