Refactor index of a rate, aka, _indexToRate
Refactor index of a rate, aka, _indexToRate

This refactor fixes an issue with 0 step

mkarajohn/react-rating,AppSorcery/react-rating,dreyescat/react-rating,AppSorcery/react-rating,mkarajohn/react-rating,AppSorcery/react-rating,mkarajohn/react-rating,dreyescat/react-rating,dreyescat/react-rating