Added CHANGELOG entry for #51
Added CHANGELOG entry for #51

Summary:
Fixed #63. I used the style we use in CocoaPods, but I'm happy to adjust!

- [x] All tests pass. Demo project builds and runs.
- [x] 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/67

Reviewed By: jessesquires

Differential Revision: D4015999

Pulled By: rnystrom

fbshipit-source-id: bbe8055f22e84c5bdc628b4c1d95dab111774e12

dshahidehpour/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,charles0126dev/IGListKit,charles0126dev/IGListKit,zhubofei/IGListKit,Sherlouk/IGListKit,Sherlouk/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,dshahidehpour/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,dshahidehpour/IGListKit,Instagram/IGListKit,Sherlouk/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,charles0126dev/IGListKit