Added the underscore node_module.

node_modules/underscore/amd/indexBy.js

@@ -0,0 +1,11 @@
+define(['./_group'], function (_group) {
+
+  // Indexes the object's values by a criterion, similar to `_.groupBy`, but for
+  // when you know that your index values will be unique.
+  var indexBy = _group(function(result, value, key) {
+    result[key] = value;
+  });
+
+  return indexBy;
+
+});