Summary:
Implements isEqual func with guard statement
- [x] All tests pass. Demo project builds and runs.
- [ ] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/CONTRIBUTING.md)
Closes https://github.com/Instagram/IGListKit/pull/151
Differential Revision: D4120016
Pulled By: rnystrom
fbshipit-source-id: a769071f788b1acc1f2fade5606859a5d91f1bfd
