请问怎么修改Express 4.x的 X-Powered-By:Express字段？

请问怎么修改Express的 X-Powered-By:Express字段？

x-powered-by Enables the “X-Powered-By: Express” HTTP header, enabled by default.

app.set('x-powered-by’, ‘xxx’’)

app.disable(‘x-powered-by’);