Custom Class: Fixed examples (#2160)

This adds a missing class to an example.

Author: RunDevelopment

plugins/custom-class/index.html

@@ -133,7 +133,7 @@ <h2>Prefix and map classes</h2>
 	&lt;span class=&quot;pr-token pr-special-keyword&quot;&gt;var&lt;/span&gt;
 	foo
 	&lt;span class=&quot;pr-token pr-operator&quot;&gt;=&lt;/span&gt;
-	&lt;span class=&quot;pr-my-string&quot;&gt;'bar'&lt;/span&gt;
+	&lt;span class=&quot;pr-token pr-my-string&quot;&gt;'bar'&lt;/span&gt;
 	&lt;span class=&quot;pr-token pr-punctuation&quot;&gt;;&lt;/span&gt;
 &lt;/code&gt;&lt;/pre&gt;</code></pre>