Summary:
The scroll delegate got lost in migrating scroll events to their own delegates and broke the sample app. It looks like there's an actual UIKit bug in iOS 10 though. Fixes#87
- [x] All tests pass. Demo project builds and runs.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/CONTRIBUTING.md)
Closes https://github.com/Instagram/IGListKit/pull/88
Differential Revision: D4050213
Pulled By: rnystrom
fbshipit-source-id: 61b29489f28002ad61193df237889b0bb8d34a29