allow string to be translated, backport from larry

skins/classic/templates/about.html

@@ -25,7 +25,7 @@ Some <a href="http://roundcube.net/license">exceptions</a> for skins &amp; plugi
 <p class="links"><roundcube:object name="supportlink" label="support" target="_blank" /></p>
 </div>
 
-<h4>Installed plugins</h4>
+<h3><roundcube:label name="installedplugins" en_US="Installed plugins" /></h3>
 <roundcube:object name="pluginlist" id="pluginlist" class="records-table" cellspacing="0" />
 
 </div>