[AIRFLOW-5574] Fix Google Analytics script loading (#6218)

docs/templates/footer.html

@@ -31,7 +31,14 @@
         ga.src = ('https:' == document.location.protocol ?
           'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
         ga.setAttribute('async', 'true');
-        document.documentElement.firstChild.appendChild(ga);
+        var nodes = document.documentElement.childNodes;
+        var i = -1;
+        var node;
+        do {
+          i++;
+          node = nodes[i]
+        } while(node.nodeType !== Node.ELEMENT_NODE);
+        node.appendChild(ga);
       })();
     </script>
   </div>