Add `require` to list of modules to try fixing kernel.js loading.

This would likely fix some failures ithat happend with `kernel.js` with
the following on the js console:

> Uncaught (in promise) TypeError: require is not a function

At

> KernelSelector._spec_changed

notebook/static/notebook/js/kernelselector.js

@@ -6,7 +6,8 @@ define([
     'base/js/namespace',
     'base/js/dialog',
     'base/js/utils',
-], function($, IPython, dialog, utils) {
+    'require',
+], function($, IPython, dialog, utils, require) {
     "use strict";
     
     var KernelSelector = function(selector, notebook) {