Bump superdesk-planning from 0c6ef8b to c877e51 in /client (#332)

Bumps [superdesk-planning](https://github.com/superdesk/superdesk-planning) from `0c6ef8b` to `c877e51`.
- [Release notes](https://github.com/superdesk/superdesk-planning/releases)
- [Commits](superdesk/superdesk-planning@0c6ef8b...c877e51)

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

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