updated `Picturefill JavaScript API` in index.html
updated `Picturefill JavaScript API` in index.html

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