Use ES6 arrow function.

js/src/tooltip.js

@@ -714,7 +714,7 @@ const Tooltip = (($) => {
 
   $.fn[NAME] = Tooltip._jQueryInterface
   $.fn[NAME].Constructor = Tooltip
-  $.fn[NAME].noConflict = function () {
+  $.fn[NAME].noConflict = () => {
     $.fn[NAME] = JQUERY_NO_CONFLICT
     return Tooltip._jQueryInterface
   }