webpack fails to bundle

报错：
The CLI moved into a separate package：webpack-cli
Would you like to install webpack-cli ( That will run npm install -D webpack-cli )
( yes/No )
解决方案：

• webpack has been updated. After webpack 4.0, the command line has a separate package, webpack-cli, to install the webpack-cli package.

npm install webpack-cli -g

• Install the specified version, such as installing version 2.4.1
  

npm install [email protected] -g