run-p: command not found

after installing 'npm install webpack-dev-server -g' not able to start expressjs project.

I am using below script:

"scripts": {
    "start": "run-p watch dev-server",
    "watch": "webpack --config webpack.config.js --watch --mode development",
    "dev-server": "BABEL_ENV=dev nodemon --exec 'babel-node' src/server/index.js --config nodemon.json"
}