Fix for HTML Keyword highlighting.

The keyword highlighting in HTML code is broken if there are not attributes for a tag!

The following markdown code:

    ```html
    <div>Test</div>
    ```

will create:

    <pre>
        <code class="lang-html">
        &lt;<span class="keyword">div&gt;test&lt;/div&gt;</span>
        </code>
    </pre>

which looks like this:

&lt;__div&gt;Test&lt;/div&gt;__

instead of:

    <pre>
        <code class="lang-html">
        &lt;<span class="keyword">div</span>&gt;test&lt;<span class="keyword">/div</span>&gt;
        </code>
    </pre>

which looks like this:

&lt;__div__&gt;Test&lt;__/div__&gt;

This was pretty easy to fix by just adding the & (of &amp;gt;) as additional end besides of a space. I also changed the space to the /s regex so it also works in the (possible) case that a tag continues with a line break or a tab character.