message: Add engines field to package.json to enforce a minimum of Node 4
diff: },
  "author": "Martijn Walraven <martijn@martijnwalraven.com>",
  "license": "MIT",
  + "engines": {
  + "node": ">=4.0"
  + },
  "devDependencies": {
  "babel-cli": "^6.11.4",
  "babel-plugin-transform-runtime": "^6.12.0",
  