message: fix(observer): do not invoke getters on initial observation
  fix
diff: @@ -61,7 +61,7 @@ export class Observer {
  walk (obj: Object) {
  const keys = Object.keys(obj)
  for (let i = 0; i < keys.length; i++) {
  - defineReactive(obj, keys[i], obj[keys[i]])
  + defineReactive(obj, keys[i])
  }
  }
  @@ -145,6 +145,9 @@ export function defineReactive (
  // cater for pre-defined getter/setters
  const getter = property && property.get
  + if (!getter && arguments.length === 2) {
  + val = obj[key]
  + }
  const setter = property && property.set
  let childOb = !shallow && observe(val)
  