benchmark: use generator delegation

benchmarks/middleware.js

@@ -10,14 +10,14 @@ console.log('  %s middleware', n);
 
 while (n--) {
   app.use(function *(next){
-    yield next;
+    yield *next;
   });
 }
 
 var body = new Buffer('Hello World');
 
 app.use(function *(next){
-  yield next;
+  yield *next;
   this.body = body;
 });