fix readme build badge
fix readme build badge

Summary: Closes https://github.com/Instagram/IGListKit/pull/95

Differential Revision: D4051336

Pulled By: jessesquires

fbshipit-source-id: a9e98aadcad7f02b886169e67a8b6ddfff542474

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