get key in v-for code example

Example 1: vue v-for

<ul id="example-1">
  <li v-for="item in items" :key="item.message">
    {{ item.message }}
  </li>
</ul>

Example 2: vuejs v-for array index

<!-- To gain access to the array index: -->
<ul>
    <li v-for="(game, index) in games"></li>
</ul>
<!--
	You only want the index in specific cases. Use `:key` as
	standard. See the other greps.
-->