HTMLWriter: Fix example block newline

org/testdata/example.html

@@ -168,7 +168,8 @@ auto link, i.e. not inside <code class="verbatim">\[[square brackets]\]</code> <
 <div class="highlight"><pre>a source block without a language
 and a second line
 and a third one</pre></div>
-<pre class="example">\nan example block
+<pre class="example">
+an example block
 with multiple lines
 </pre>
 <blockquote>