add support for trailing commas in arrow function parameter lists - fixes #1841
add support for trailing commas in arrow function parameter lists - fixes #1841

jridgewell/babel,kellyselden/babel,PolymerLabs/babel,babel/babylon,guybedford/babel,hzoo/babel,guybedford/babel,hulkish/babel,existentialism/babel,hzoo/babel,hulkish/babel,guybedford/babel,chicoxyzzy/babel,Skillupco/babel,samwgoldman/babel,kellyselden/babel,kellyselden/babel,hzoo/babel,chicoxyzzy/babel,hzoo/babel,vadzim/babel,wcjohnson/babylon-lightscript,shuhei/babel,shuhei/babel,babel/babel,samwgoldman/babel,lightscript/babylon-lightscript,shuhei/babel,jridgewell/babel,Skillupco/babel,maurobringolf/babel,danez/babylon,vadzim/babel,kaicataldo/babel,kellyselden/babel,jridgewell/babel,babel/babel,recipesjs/ingredients,Skillupco/babel,babel/babel,hulkish/babel,claudiopro/babel,kaicataldo/babel,kaicataldo/babel,hulkish/babel,claudiopro/babel,existentialism/babel,cbishopvelti/babylon,maurobringolf/babel,claudiopro/babel,jridgewell/babel,chicoxyzzy/babel,PolymerLabs/babel,PolymerLabs/babel,Skillupco/babel,babel/babel,samwgoldman/babel,maurobringolf/babel,existentialism/babel,chicoxyzzy/babel,kaicataldo/babel