Strong emphasis code spans parse error

[ptpt]

This happens when I parse strong emphasized code spans.

For example, parse:

**`hello`** *`world`*

sundown's output is:

<p>*<em><code>hello</code>** *<code>world</code></em></p>

But the expected output should be:

<p><strong><code>hello</code></strong> <em><code>world</code></em></p>

[mildsunrise]

This bug has been fixed in Hoedown.