Update README
Update README

Change Coveralls tag to master branch
heitortsergent/KeenClient-iOS,heitortsergent/KeenClient-iOS,keenlabs/KeenClient-iOS,heitortsergent/KeenClient-iOS,keenlabs/KeenClient-iOS,heitortsergent/KeenClient-iOS,keenlabs/KeenClient-iOS,heitortsergent/KeenClient-iOS