Added the underscore node_module.

node_modules/underscore/modules/_group.js

@@ -0,0 +1,15 @@
+import cb from './_cb.js';
+import each from './each.js';
+
+// An internal function used for aggregate "group by" operations.
+export default function group(behavior, partition) {
+  return function(obj, iteratee, context) {
+    var result = partition ? [[], []] : {};
+    iteratee = cb(iteratee, context);
+    each(obj, function(value, index) {
+      var key = iteratee(value, index, obj);
+      behavior(result, value, key);
+    });
+    return result;
+  };
+}