Library does not compile under swift 4

[gastrodon]

Output: https://pastebin.com/Ey1pDyVu

main.swift:

print("Hello, world!")

Package.swift:

import PackageDescription

let package = Package(
    name: "PinSwift",
    dependencies: [
        .package(url: "https://github.com/eonist/Element.git", .branch("master"))
    ],
    targets: [
        .target(
            name: "PinSwift",
            dependencies: [
                "Element",
            ],
            path: "Sources"
        ),
        .testTarget(
            name: "PinSwiftTests",
            dependencies: ["PinSwift"]),
    ]
)

AppDelegate.swift is empty

If I'm importing the library wrong, please let me know. It doesn't work in Package.swift the way mentioned in README.md, so I've changed that