Unresolved identifier NavigationButton error

NavigationLink replace NavigationButton, The code below is update for WWDC 2019 Introducing SwiftUI: Building Your First App

struct RoomCell: View {
    let room: Room

    var body: some View {
        NavigationLink(destination: RoomDetail(room: room)) {
            Image(room.thumbnailName)
                .cornerRadius(8)
            VStack(alignment: .leading) {
                Text(room.name)
                Text("\(room.capacity) people")
                    .font(.subheadline)
                    .foregroundColor(.secondary)
            }
        }
    }
}

NavigationButton changed to NavigationLink for a while now. So replace it and use it.