build vuejs with new config mode with production build

 ## When you want to use another config values in deploying. you must add NODE_ENV=production

## .env.mynewmode

   NODE_ENV=production                 ##<-- this line makes files for deploying 

   VUE_APP_MY_VAR='mynewvalue' 

## build

npm run build -- --mode mynewmode

#ref: https://cli.vuejs.org/guide/mode-and-env.html#modes

https://cli.vuejs.org/guide/mode-and-env.html#modes