Fix init for ORKKeyValueStepModifier
Fix init for ORKKeyValueStepModifier

jeremiahyan/ResearchKit,mluedke2/ResearchKit,jeremiahyan/ResearchKit,mluedke2/ResearchKit,md0u80c9/ResearchKit,chb/ResearchKit,mluedke2/ResearchKit,chb/ResearchKit,md0u80c9/ResearchKit,jeremiahyan/ResearchKit,md0u80c9/ResearchKit,chb/ResearchKit,chb/ResearchKit,md0u80c9/ResearchKit