Added the underscore node_module.

node_modules/underscore/cjs/groupBy.js

@@ -0,0 +1,10 @@
+var _group = require('./_group.js');
+var _has = require('./_has.js');
+
+// 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];
+});
+
+module.exports = groupBy;