Support 'spec' option on babel-preset-es2015 (#3671)
Support 'spec' option on babel-preset-es2015 (#3671)

Allows enabling the spec options in the couple of presets that have it.

Generally enables a slower, but more correct codepath.
kellyselden/babel,kaicataldo/babel,zertosh/babel,kedromelon/babel,samwgoldman/babel,ccschneidr/babel,guybedford/babel,iamchenxin/babel,kaicataldo/babel,maurobringolf/babel,hzoo/babel,KunGha/babel,lxe/babel,shuhei/babel,lxe/babel,existentialism/babel,zertosh/babel,tikotzky/babel,hulkish/babel,ccschneidr/babel,jridgewell/babel,Skillupco/babel,guybedford/babel,iamchenxin/babel,jridgewell/babel,claudiopro/babel,kaicataldo/babel,vadzim/babel,bcoe/babel,babel/babel,rmacklin/babel,babel/babel,zjmiller/babel,chicoxyzzy/babel,kellyselden/babel,garyjN7/babel,PolymerLabs/babel,tikotzky/babel,jridgewell/babel,STRML/babel,babel/babel,chicoxyzzy/babel,maurobringolf/babel,existentialism/babel,jridgewell/babel,iamchenxin/babel,hzoo/babel,hzoo/babel,kaicataldo/babel,rmacklin/babel,hulkish/babel,babel/babel,Skillupco/babel,garyjN7/babel,PolymerLabs/babel,kellyselden/babel,hzoo/babel,KunGha/babel,existentialism/babel,kassens/babel,shuhei/babel,kellyselden/babel,claudiopro/babel,claudiopro/babel,kassens/babel,maurobringolf/babel,vadzim/babel,kedromelon/babel,jchip/babel,kedromelon/babel,samwgoldman/babel,hulkish/babel,bcoe/babel,zjmiller/babel,shuhei/babel,Skillupco/babel,Skillupco/babel,samwgoldman/babel,jchip/babel,PolymerLabs/babel,STRML/babel,hulkish/babel,chicoxyzzy/babel,chicoxyzzy/babel,guybedford/babel