Changed an example for nested loop in List Rendering (#2441)

* fix: changed an example for nested loop

* fix: fixed example to be ES5

Author: NataliaTepluhina

src/v2/guide/list.md

@@ -383,13 +383,15 @@ computed: {
 
 In situations where computed properties are not feasible (e.g. inside nested `v-for` loops), you can use a method:
 
-``` html
-<li v-for="n in even(numbers)">{{ n }}</li>
+```html
+<ul v-for="set in sets">
+  <li v-for="n in even(set)">{{ n }}</li>
+</ul>
 ```
 
-``` js
+```js
 data: {
-  numbers: [ 1, 2, 3, 4, 5 ]
+  sets: [[ 1, 2, 3, 4, 5 ], [6, 7, 8, 9, 10]]
 },
 methods: {
   even: function (numbers) {