fix two-way binding change propagation bug (#460)
fix two-way binding change propagation bug (#460)

ractivejs/ractive,JonDum/ractive,ISNIT0/ractive,heavyk/ractive,heavyk/ractive,ndimas/ractive,thomsbg/ractive,pingjiang/ractive,pingjiang/ractive,cgvarela/ractive,magicdawn/ractive,aliprogrammer69/ractive,aliprogrammer69/ractive,JonDum/ractive,marcalexiei/ractive,p0lax/ractive,pingjiang/ractive,Rich-Harris/ractive,magicdawn/ractive,ndimas/ractive,npmcomponent/RactiveJS-Ractive,dyx/ractive,squaredup/ractive,Rich-Harris/ractive,thomsbg/ractive,npmcomponent/RactiveJS-Ractive,squaredup/ractive,squaredup/ractive,ractivejs/ractive,cgvarela/ractive,heavyk/ractive,dyx/ractive,p0lax/ractive,ISNIT0/ractive,ISNIT0/ractive,cgvarela/ractive,dyx/ractive,thomsbg/ractive,aliprogrammer69/ractive,ractivejs/ractive,ndimas/ractive,JonDum/ractive,marcalexiei/ractive,Rich-Harris/ractive,marcalexiei/ractive,magicdawn/ractive