classlist fix

Author: adamschwartz

js/install.js

@@ -3,6 +3,6 @@
 
   Array.prototype.forEach.call(document.querySelectorAll('table'), function(table){
     table.setAttribute('data-sortable', '');
-    table.add('sortable-theme-' + options.theme);
+    table.classList.add('sortable-theme-' + options.theme);
   });
 })();