[react] react version not specified in eslint-plugin-react settings

https://github.com/yannickcr/eslint-plugin-react/issues/2157

npm start 時, 在 terminal 中報的 warning 信息: react version not specified in eslint-plugin-react settings

解決方案是在 .eslintrc中添加配置:

"settings": {
    "react": {
      "version": "detect"
    }
  }

done.