Added the underscore node_module.

node_modules/underscore/modules/_cb.js

@@ -0,0 +1,10 @@
+import _ from './underscore.js';
+import baseIteratee from './_baseIteratee.js';
+import iteratee from './iteratee.js';
+
+// The function we call internally to generate a callback. It invokes
+// `_.iteratee` if overridden, otherwise `baseIteratee`.
+export default function cb(value, context, argCount) {
+  if (_.iteratee !== iteratee) return _.iteratee(value, context);
+  return baseIteratee(value, context, argCount);
+}