Update robots.txt (#168)

This should ignore URLs with query params.

Source: https://stackoverflow.com/questions/9149782/ignore-urls-in-robot-txt-with-specific-parameters

Author: XhmikosR

docs/robots.txt

@@ -6,5 +6,5 @@ layout: null
 
 # Allow crawling of all content
 User-agent: *
-Disallow:
+Disallow: /*?*
 Sitemap: {{ site.url }}/sitemap.xml