Update CHANGELOG for v6.7.7.
Update CHANGELOG for v6.7.7.

zjmiller/babel,chicoxyzzy/babel,maurobringolf/babel,jridgewell/babel,hzoo/babel,bcoe/babel,tikotzky/babel,iamchenxin/babel,vadzim/babel,jhen0409/babel,Skillupco/babel,tikotzky/babel,iamchenxin/babel,kedromelon/babel,samwgoldman/babel,jridgewell/babel,hulkish/babel,PolymerLabs/babel,kedromelon/babel,Skillupco/babel,KunGha/babel,PolymerLabs/babel,ccschneidr/babel,kellyselden/babel,zertosh/babel,antn/babel,shuhei/babel,STRML/babel,jridgewell/babel,chicoxyzzy/babel,jridgewell/babel,hulkish/babel,antn/babel,STRML/babel,zertosh/babel,bcoe/babel,babel/babel,maurobringolf/babel,existentialism/babel,vadzim/babel,iamchenxin/babel,guybedford/babel,babel/babel,kellyselden/babel,shuhei/babel,rmacklin/babel,garyjN7/babel,kaicataldo/babel,claudiopro/babel,ccschneidr/babel,chicoxyzzy/babel,Skillupco/babel,guybedford/babel,babel/babel,guybedford/babel,kaicataldo/babel,KunGha/babel,garyjN7/babel,Skillupco/babel,maurobringolf/babel,kassens/babel,existentialism/babel,hulkish/babel,chicoxyzzy/babel,jchip/babel,rmacklin/babel,kellyselden/babel,existentialism/babel,lxe/babel,shuhei/babel,hulkish/babel,jhen0409/babel,babel/babel,lxe/babel,claudiopro/babel,kaicataldo/babel,PolymerLabs/babel,kaicataldo/babel,zjmiller/babel,samwgoldman/babel,hzoo/babel,claudiopro/babel,kellyselden/babel,samwgoldman/babel,jchip/babel,kedromelon/babel,hzoo/babel,hzoo/babel,kassens/babel