Release 5.0.2 including latest Firebase SDK compatibility updates

Commit [bd254cb](https://github.com/firebase/geofire-objc/commit/bd254cb08948dcedf5c16b51fa78852772221572) added support for Firebase SDK versions `<13`, but the latest published release (5.0.1) still restrict the SDK to `<12`.

Using `master` directly works just fine, but it would be helpful to publish a new patch or minor release that includes this update.

Thanks in advance, and please let me know if I can help with anything to get this out.