message: remove parent/ref elm references when destroying instance, fix memory leak (fix vue-router#1279)
diff: @@ -119,6 +119,9 @@ export function lifecycleMixin (Vue: Class<Component>) {
  }
  // call the last hook...
  vm._isDestroyed = true
  + // invoke destroy hooks on current rendered tree
  + vm.__patch__(vm._vnode, null)
  + // fire destroyed hook
  callHook(vm, 'destroyed')
  // turn off all instance listeners.
  vm.$off()
  @@ -126,8 +129,8 @@ export function lifecycleMixin (Vue: Class<Component>) {
  if (vm.$el) {
  vm.$el.__vue__ = null
  }
  - // invoke destroy hooks on current rendered tree
  - vm.__patch__(vm._vnode, null)
  + // remove reference to DOM nodes (prevents leak)
  + vm.$options._parentElm = vm.$options._refElm = null
  }
  }
  