update vue version npm

npm install -g vue-cli    //make sure you have node and npm installed 
vue init webpack <appname>  //  eg:  vue init webpack myapp
cd <appname>               // cd myapp
npm install
npm run dev  //server will start in port 8080npm install -g @vue/cli
# OR
yarn global add @vue/cli
npm install -g @vue/cli --save

# OR
yarn global upgrade --latest @vue/cli