fix admin/customize page DOM and header

lib/views/admin/customize.html

@@ -3,6 +3,7 @@
 {% block html_title %}{{ t('Customize') }} {% endblock %}
 
 {% block html_additional_headers %}
+  {% parent %}
   <!-- CodeMirror -->
   <link rel="stylesheet" href="https://cdn.jsdelivr.net/g/codemirror@4.5.0(codemirror.css+addon/hint/show-hint.css)">
   <link rel="stylesheet" href="https://cdn.jsdelivr.net/jquery.ui/1.11.4/jquery-ui.min.css">
@@ -215,7 +216,7 @@
 
         <p class="help-block">
           Examples:
-          <pre><code>&lt;script src="https://cdn.jsdelivr.net/gh/highlightjs/cdn-release@9.12.0/build/languages/yaml.min.js" defer&gt;&lt;/script&gt;</script></code></pre>
+          <pre><code>&lt;script src="https://cdn.jsdelivr.net/gh/highlightjs/cdn-release@9.12.0/build/languages/yaml.min.js" defer&gt;&lt;/script&gt;</code></pre>
         </p>
 
         <div class="form-group">