Tags within pre blocks cause nōn-pre rendering of their contents

[mirabilos]

Related to #103 but different:

>>> from markdownify.markdownify import markdownify
>>> print(markdownify('<pre>foo*bar</pre>'))

```
foo*bar
```

>>> print(markdownify('<pre>foo<span class="asterix">*</span>bar</pre>'))

```
foo\*bar
```

I expect them to convert identical.

[mirabilos]

Oh, nice, fixed by #104, thanks!