Kramdown with rogue didn't generate <pre> wrapper
<p>This is from my pry console:</p>

<pre><code>&gt; input = &lt;&lt;-HEREDOC
* # Header 1
* ## Header 2
*
* ```
* def hello
*   puts "hello world"
* end
* ```
* HEREDOC
=&gt; "# Header 1\n## Header 2\n\n```\ndef hello\n  puts \"hello world\"\nend\n```\n"
&gt; Kramdown::Document.new(input, input: "GFM", syntax_highlighter: "rouge").to_html
=&gt; "&lt;h1 id=\"header-1\"&gt;Header 1&lt;/h1&gt;\n&lt;h2 id=\"header-2\"&gt;Header 2&lt;/h2&gt;\n\n&lt;div class=\"highlighter-rouge\"&gt;def hello\n  puts \"hello world\"\nend\n&lt;/div&gt;\n"
</code></pre>

<p>As you can see, the html generated for the code block doesn't contain any <code>&lt;pre&gt;</code> code wrapper. But if I removed <code>rouge</code> option and use <code>coderay</code>, it works beautifully.</p>

<pre><code>&gt; Kramdown::Document.new(input, input: "GFM").to_html
=&gt; "&lt;h1 id=\"header-1\"&gt;Header 1&lt;/h1&gt;\n&lt;h2 id=\"header-2\"&gt;Header 2&lt;/h2&gt;\n\n&lt;pre&gt;&lt;code&gt;def hello\n  puts \"hello world\"\nend\n&lt;/code&gt;&lt;/pre&gt;\n"
</code></pre>

<p>Any idea what's wrong? Thanks in advance.</p>