Minor update to HTML reporter's CSS.

Previously the HTML reporter displayed 'pre' blocks with display set to 'inline-block', however given a wide enough screen, when a test fails and you click the h2, the code snippet will display beside the error output (with whitespace being introduced directly below the test heading), as opposed to below it which would look more consistent. This commit fixes this styling.

Here's a screenshot illustrating the issue before the fix:
![Screen Shot 2013-01-08 at 13 25 09](https://f.cloud.github.com/assets/974125/50183/f83cd97c-5996-11e2-845a-265e40f9bd69.png)

After applying this fix, the code preview is shown directly below the error output as expect.