Update jquery version for bootstrap compatibility

Author: jdomingu

docs/_includes/head.html

@@ -11,5 +11,5 @@
   <link rel="stylesheet" href="{{ site.baseurl }}/css/main.css">
   <link rel="stylesheet" href="{{ site.baseurl }}/css/github-highlight.css">
 
-  <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
+  <script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
   <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>