Added the underscore node_module.

node_modules/underscore/cjs/_group.js

@@ -0,0 +1,17 @@
+var _cb = require('./_cb.js');
+var each = require('./each.js');
+
+// An internal function used for aggregate "group by" operations.
+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;
+  };
+}
+
+module.exports = group;