Fix build on macOS

Author: kateinoigakukun

Plugins/PackageToJS/Package.swift

@@ -4,6 +4,7 @@ import PackageDescription
 
 let package = Package(
     name: "PackageToJS",
+    platforms: [.macOS(.v13)],
     targets: [
         .target(name: "PackageToJS"),
         .testTarget(name: "PackageToJSTests", dependencies: ["PackageToJS"]),