Enable CORS for Disqus script

Author: rcvalle

_includes/disqus.html

@@ -1,6 +1,6 @@
 {% if site.disqus_shortname %}
   <div id="disqus_thread"></div>
-  <script>
+  <script crossorigin="anonymous">
       var disqus_config = function () {
           this.page.url = '{{ page.url | absolute_url }}';
           this.page.identifier = '{{ page.url | relative_url }}';