Fix template syntax.

Doc/tools/sphinxext/layout.html

@@ -8,7 +8,7 @@
 {% block extrahead %}
     <link rel="shortcut icon" type="image/png" href="{{ pathto('_static/py.png', 1) }}" />
     {% if not embedded %}<script type="text/javascript" src="{{ pathto('_static/copybutton.js', 1) }}"></script>{% endif %}
-    {% if pagename == 'whatsnew/changelog %}
+    {% if pagename == 'whatsnew/changelog' %}
     <script type="text/javascript">
       function dofilter() {
         var el = document.getElementById('searchbox');