[iOS] Bump up the cocoapods version (#41895)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41895
### Summary
The iOS binary for 1.6.0 has been uploaded to AWS. This PR bumps up the version for cocoapods.
### Test Plan
- Check CI
Test Plan: Imported from OSS
Reviewed By: husthyc
Differential Revision: D22683787
Pulled By: xta0
fbshipit-source-id: bb95b670a7945d823d55e9c65b357765753f295a
