Fixed some more typos in README
Fixed some more typos in README

StevenLangbroek/reactfire,timotius02/reactfire,ronlobo/reactfire,FirebaseExtended/reactfire,FirebaseExtended/reactfire,chiefr/reactfire,StevenLangbroek/reactfire,FirebaseExtended/reactfire,Shraymonks/reactfire,gragland/reactfire,FirebaseExtended/reactfire,ramyathulasingam/reactfire,carlosCeron/reactfire,Wattenberger/reactfire,Wattenberger/reactfire,chiefr/reactfire