[2.0]Lost whitespace in `<pre><code> </code></pre>`

[QingWei-Li]

Vue.js version

2.0.0-beta.5

Reproduction Link

https://jsbin.com/guyudu/edit?html,js,output

Steps to reproduce

template

  <div>
  This is correct.

  <pre>
    <span>1. Hello</span>
    <span>2. Vue</span>
  </pre>

  This is incorrect. Lost whitespace

  <pre>
    <code>
      <span>1. Hello</span>
      <span>2. Vue</span>
    </code>
  </pre>
</div>

What is Expected?

        1. Hello
        2. Vue

What is actually happening?

     1. Hello 2. Vue