webpack-dotenv v0.0.3

import WebpackDotEnv from 'webpack-dotenv';

{
  plugins: [
    new WebpackDotEnv({
      NODE_ENV: process.env.NODE_ENV,
    }),
  ] 
}

you can create any dot env file regarding to NODE_ENV 
.env 
.env.development
.env.production
.env.stage