webpack-dev-server: コマンドが見つかりませんの対処法 #webpack

> webpack-dev-server -d --config webpack.dev.config.js --content-base public/ --progress --colors

sh: webpack-dev-server: command not found

npm ERR! Darwin 14.4.0
npm ERR! argv "node" "/usr/local/bin/npm" "run" "devserve"
npm ERR! node v0.12.4
npm ERR! npm  v2.10.1
npm ERR! file sh
npm ERR! code ELIFECYCLE
npm ERR! errno ENOENT
npm ERR! syscall spawn
npm ERR! Blabber@0.0.1 devserve: `webpack-dev-server -d --config webpack.dev.config.js --content-base public/ --progress --colors`
npm ERR! spawn ENOENT

こんなエラーがでたら、

$ npm install webpack-dev-server -g