Added the underscore node_module.

node_modules/underscore/amd/difference.js

@@ -0,0 +1,14 @@
+define(['./restArguments', './_flatten', './filter', './contains'], function (restArguments, _flatten, filter, contains) {
+
+  // Take the difference between one array and a number of other arrays.
+  // Only the elements present in just the first array will remain.
+  var difference = restArguments(function(array, rest) {
+    rest = _flatten(rest, true, true);
+    return filter(array, function(value){
+      return !contains(rest, value);
+    });
+  });
+
+  return difference;
+
+});