https://medium.com/%E5%BD%BC%E5%BE%97%E6%BD%98%E7%9A%84-swift-ios-app-%E9%96%8B%E7%99%BC%E6%95%99%E5%AE%A4/swift-practice-107-firebase%E5%88%9D%E6%8E%A2-cocoapods%E5%AE%89%E8%A3%9D%E8%88%87%E7%92%B0%E5%A2%83%E8%A8%AD%E5%AE%9A-73e03ab599e3
