Fixed a markdown issue

Maybe a bug in SS markdown?

The old code generated:
<a href="(faulty-link)">assertEmailSent</a>
<code>which can simulate sending emails through the</code>Email-&gt;send()` API

Instead of the expected:
<code><a href="(good-link)">assertEmailSent</a></code>
which can simulate sending emails through the <code>Email-&gt;send()</code> API

faulty-link = http://api.silverstripe.org/search/lookup/?q=SapphireTest->assertEmailSent(&version=trunk&module=framework)

good-link: http://api.silverstripe.org/search/lookup/?q=SapphireTest->assertEmailSent()&version=trunk&module=framework