Add env option to babel-preset-react-app

Created by: donocode

Addresses: #2592 (closed)

Summary

Adds possibility to specify env/environment option directly to babel-preset-react-app

Examples

"babel": {
    "presets": [
      [ "react-app", { "env": "development" } ]
    ]
  }

"babel": {
    "presets": [
      [ "react-app", { "environment": "production" } ]
    ]
  },

Changes

Code changes are simple, wrap the current preset in a function to allow opts to be specified, plugins are now returned from the function instead of being exported directly