Update CONTRIBUTING.md
Update CONTRIBUTING.md
yubin-huang/picturefill,guardian/picturefill,yufi113/picturefill,scottjehl/picturefill,yufi113/picturefill,demateu/picturefill,purposeindustries/picturefill,iancrowther/picturefill,yubin-huang/picturefill,iancrowther/picturefill,albell/picturefill,samiadelgado/picturefill,samiadelgado/picturefill,albell/picturefill,rockmandew/picturefill,mcanthony/picturefill,ddeveloperr/picturefill,footiealf/picturefill,patrickkettner/picturefill,chrismcandrew/picturefill,ddeveloperr/picturefill,purposeindustries/picturefill,patrickkettner/picturefill,chrismcandrew/picturefill,mcanthony/picturefill,scottjehl/picturefill,footiealf/picturefill,demateu/picturefill,guardian/picturefill,rockmandew/picturefill