Exclude /dart/ subtree from crawling.

Author: armiol

robots.txt

@@ -6,4 +6,5 @@ User-agent: *
 {% for node in site.pages %}{% if node.noindex %}{% assign isset = true %}Disallow: {{ node.url }}
 {% endif %}{% endfor %}{% if isset != true %}Disallow:
 {% endif %}
+Disallow: /dart/
 Sitemap: {{site.url}}{{ site.baseurl }}/sitemap.xml