New line in code block breaks them

[IncandescentChrysalis]

Describe the bug
Code blocks containing new lines are not recognised as such.

To Reproduce

```
<my code>

<Test>
```

Observed behavior

<p>```
<my code></p>

<p><Test>
```</p>

Expected behavior

<p><code>
&lt;my code&gt;

&lt;Test&gt;
</code></p>

Debug info
Version of library being used:

• markdown2==2.4.13

Additional context
The same block without new line:

```
<my code>
<Test>
```

works fine:

<p><code>
&lt;my code&gt;
&lt;Test&gt;
</code></p>

[IncandescentChrysalis]

Resolved by using the fenced-code-blocks extra.