demo from ’Object Change Detection‘ doesn't work (#1397)

vm.$set(this.userProfile, 'age', 27)    ==>   vm.$set(vm.userProfile, 'age', 27);

Author: frankwang0909

src/v2/guide/list.md

@@ -322,13 +322,13 @@ Vue.set(vm.userProfile, 'age', 27)
 You can also use the `vm.$set` instance method, which is an alias for the global `Vue.set`:
 
 ``` js
-vm.$set(this.userProfile, 'age', 27)
+vm.$set(vm.userProfile, 'age', 27)
 ```
 
 Sometimes you may want to assign a number of new properties to an existing object, for example using `Object.assign()` or `_.extend()`. In such cases, you should create a fresh object with properties from both objects. So instead of:
 
 ``` js
-Object.assign(this.userProfile, {
+Object.assign(vm.userProfile, {
   age: 27,
   favoriteColor: 'Vue Green'
 })
@@ -337,7 +337,7 @@ Object.assign(this.userProfile, {
 You would add new, reactive properties with:
 
 ``` js
-this.userProfile = Object.assign({}, this.userProfile, {
+vm.userProfile = Object.assign({}, vm.userProfile, {
   age: 27,
   favoriteColor: 'Vue Green'
 })