html: Fix example blocks - escape html

While example blocks do not render inline markup and are thus parsed raw in
some way, their contents are not literal html and thus still need to be html
escaped.

org/testdata/misc.html

@@ -200,7 +200,7 @@ example block
 </p>
 <pre class="example">
 language: go
-go: "1.x"
+go: &#34;1.x&#34;
 script:
   - make test
   - make generate-gh-pages