webpack打包问题

我是这么写的

module.exports = {

    entry: './src/app.js',

    output: {

        path: './bin/',

        filename: 'app.bundle.js'

    }

};

报错：

Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.

 - configuration.output.path: The provided value "./bin/" is not an absolute path!

我看到视频和webpack 官网都是这么写的 怎么在我这就报错呢 想不明白，希望大神们给指点下，谢谢