Added the underscore node_module.

node_modules/underscore/modules/union.js

@@ -0,0 +1,9 @@
+import restArguments from './restArguments.js';
+import uniq from './uniq.js';
+import flatten from './_flatten.js';
+
+// Produce an array that contains the union: each distinct element from all of
+// the passed-in arrays.
+export default restArguments(function(arrays) {
+  return uniq(flatten(arrays, true, true));
+});