Cannot find module ‘webpack-cli/bin/config-yargs’ :

Webpack is not compatible with the webpack-dev-server version:

Under this vue project, type :
npm uninstall  webpack -g
npm uninstall -g webpack-dev-server
Uninstall and reinstall:
npm install webpack@3.8.0 --save-dev
npm install webpack-dev-server@2.9.7 --save-dev

Restart the project, success!