Header name must be a valid http token? Что делать?

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader('content-type', 'text/plain');
res.end('Hello world!');
});

server.listen(port, hostname, () => {
console.log("Server started");
});

https://pp.userapi.com/c850032/v850032824/58134/F7...