Added the underscore node_module.

node_modules/underscore/amd/invert.js

@@ -0,0 +1,15 @@
+define(['./keys'], function (keys) {
+
+  // Invert the keys and values of an object. The values must be serializable.
+  function invert(obj) {
+    var result = {};
+    var _keys = keys(obj);
+    for (var i = 0, length = _keys.length; i < length; i++) {
+      result[obj[_keys[i]]] = _keys[i];
+    }
+    return result;
+  }
+
+  return invert;
+
+});