fix string name for backend store class
fix string name for backend store class

ismaelgaudioso/Coherence,unintended/Cohen,furbrain/Coherence,sreichholf/python-coherence,furbrain/Coherence,opendreambox/python-coherence,ismaelgaudioso/Coherence,coherence-project/Coherence,unintended/Cohen,coherence-project/Coherence,sreichholf/python-coherence,opendreambox/python-coherence