Bump superdesk-core from 87c8806 to c9751a2 in /client

Bumps [superdesk-core](https://github.com/superdesk/superdesk-client-core) from `87c8806` to `c9751a2`.
- [Release notes](https://github.com/superdesk/superdesk-client-core/releases)
- [Commits](superdesk/superdesk-client-core@87c8806...c9751a2)

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

Signed-off-by: dependabot[bot] <[email protected]>