Update benchmark, remove --harmony flag and use arrow functions

closes #567

Fix benchmark middleware - in promises body is on ctx not on this

benchmarks/middleware.js

@@ -11,17 +11,11 @@ let n = parseInt(process.env.MW || '1', 10);
 console.log(`  ${n} middleware`);
 
 while (n--) {
-  app.use(function(ctx, next){
+  app.use((ctx, next) => next());
-    return next();
-  });
 }
 
 const body = new Buffer('Hello World');
 
-app.use(function(ctx, next){
+app.use((ctx, next) => next().then(() => ctx.body = body));
-  return next().then(function(){
-    this.body = body;
-  });
-});
 
 app.listen(3333);

benchmarks/run

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 echo
-MW=$1 node --harmony $2 &
+MW=$1 node $2 &
 pid=$!
 
 sleep 2