Added the underscore node_module.

node_modules/underscore/amd/groupBy.js

@@ -0,0 +1,11 @@
+define(['./_group', './_has'], function (_group, _has) {
+
+  // Groups the object's values by a criterion. Pass either a string attribute
+  // to group by, or a function that returns the criterion.
+  var groupBy = _group(function(result, value, key) {
+    if (_has(result, key)) result[key].push(value); else result[key] = [value];
+  });
+
+  return groupBy;
+
+});