Put server process.env.NODE_ENV check back

When you deploy app to Heroku, and you forget to set NODE_ENV
environment variable, this will warn you. Of course you have to set to
production on Heroku.
require('babel-register');

const serverConfig = require('./config');
const WebpackIsomorphicTools = require('webpack-isomorphic-tools');
const webpackIsomorphicAssets = require('../../webpack/assets');
const rootDir = require('path').resolve(__dirname, '..', '..');

if (!process.env.NODE_ENV)
  throw new Error(
    'Environment variable NODE_ENV must be set to development or production.'
  );

// http://formatjs.io/guides/runtime-environments/#polyfill-node
if (global.Intl) {
  // We don't have to check whether Node runtime supports specific language,
  // because without special build it does support only english anyway.
  require('intl');
  global.Intl.NumberFormat = global.IntlPolyfill.NumberFormat;
  global.Intl.DateTimeFormat = global.IntlPolyfill.DateTimeFormat;
} else {
  global.Intl = require('intl');
}

global.webpackIsomorphicTools = new WebpackIsomorphicTools(webpackIsomorphicAssets)
  .development(!serverConfig.isProduction)
  .server(rootDir, () => {
    require('./main');
  });

require('babel-register');

const serverConfig = require('./config');
const WebpackIsomorphicTools = require('webpack-isomorphic-tools');
const webpackIsomorphicAssets = require('../../webpack/assets');
const rootDir = require('path').resolve(__dirname, '..', '..');

// if (!process.env.NODE_ENV)
//   throw new Error('Environment variable NODE_ENV isn\'t set. Remember it\'s up your production enviroment to set NODE_ENV and maybe other variables.');

// http://formatjs.io/guides/runtime-environments/#polyfill-node
if (global.Intl) {
  // We don't have to check whether Node runtime supports specific language,
  // because without special build it does support only english anyway.
  require('intl');
  global.Intl.NumberFormat = global.IntlPolyfill.NumberFormat;
  global.Intl.DateTimeFormat = global.IntlPolyfill.DateTimeFormat;
} else {
  global.Intl = require('intl');
}

global.webpackIsomorphicTools = new WebpackIsomorphicTools(webpackIsomorphicAssets)
  .development(!serverConfig.isProduction)
  .server(rootDir, () => {
    require('./main');
  });
