title: How can I bind the html <title> content in vuejs?
body: <p>I'm trying a demo on vuejs. Now I want the html title to bind a vm field.</p>
  
  <p>The below is what I tried:</p>
  
  <p><code>index.html</code></p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html id="html"&gt;
  &lt;head&gt;
      &lt;title&gt;{{ hello }}&lt;/title&gt;
      &lt;script src="lib/requirejs/require.min.js" data-main="app"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  {{ hello }}
  &lt;input v-model="hello" title="hello" /&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p><code>app.js</code></p>
  
  <pre><code>define([
      'jquery', 'vue'
  ], function ($, Vue) {
      var vm = new Vue({
          el: 'html',
          data: {
              hello: 'Hello world'
          }
      });
  });
  </code></pre>
  
  <p>But the title seemed not bounded, how to make it work?</p>