Add req/res to res.locals not global nunjucks instance

lib/nunjucks-middleware.js

@@ -1,7 +1,5 @@
 module.exports = (req, res, next) => {
-  req.app.settings.nunjucksEnv
-    .addGlobal('req', req)
-    .addGlobal('res', res);
-
+  res.locals.req = req;
+  res.locals.res = res;
   next();
 }