[Vuejs]-Vue.js template do not shows the data

You document version is 1.x, and you use the vue.js CDN version is 2.5.13:

<script type="text/javascript" src="https://cdn.bootcss.com/vue/2.5.13/vue.min.js"></script>

The {{* }} syntax is removed in Vue 2.x, you can use v-once to replace it:

<div id="app" v-once>
  this will never change:{{ msg }}
</div>