Update CHANGELOG.md
Update CHANGELOG.md

Summary:
For the sake of completion I added commit/pr numbers to the rest of the changelog
Finishes https://github.com/Instagram/IGListKit/issues/278

- [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/.github/CONTRIBUTING.md)
- [x] Have a real need to complete minor things
Closes https://github.com/Instagram/IGListKit/pull/293

Differential Revision: D4286735

Pulled By: jessesquires

fbshipit-source-id: 907eec77cc54086daeb52c7c23a097c74f6d0422

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