Add compatibility support for keyf in group command
Add compatibility support for keyf in group command

saintedlama/mongojs,AMKohn/mongojs,Dcardcc/mongojs,PaulinePro/mongojs,octoblu/mongojs,mafintosh/mongojs,Dcard/mongojs,litixsoft/mongojs,JaKXz/promised-mongo,beni55/mongojs,lionvs/mongojs,kapetan/mongojs,gordonmleigh/promised-mongo,tapsboy/promised-mongo