I’m trying to specify the minimum OS version using the platforms field in Package.swift, but I’m getting an error:

$ swift package init --type=executable
$ vim Package.swift
$ swift build
error: manifest parse error(s):
/Users/alexmerenstein/Testing/Package.swift:6:22: error: incorrect argument label in call (have 'name:platforms:dependencies:targets:', expected 'name:pkgConfig:dependencies:targets:')
let package = Package(
                     ^

Package.swift:

// swift-tools-version:4.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "message-bridge",
    platforms: [
        .macOS(.v10_12)
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
        .target(
            name: "MessageBridgeTest",
        )
    ]
)