add engines field

package.json

@@ -10,6 +10,10 @@
     "build:client": "cross-env NODE_ENV=production webpack --config build/webpack.client.config.js --progress --hide-modules",
     "build:server": "cross-env NODE_ENV=production webpack --config build/webpack.server.config.js --progress --hide-modules"
   },
+  "engines": {
+    "node": ">=6.0",
+    "npm": ">=3.0"
+  },
   "dependencies": {
     "compression": "^1.6.2",
     "es6-promise": "^3.2.1",