Add macOS from devicekit#217

Author: the-yuyut

Package.swift

@@ -17,7 +17,8 @@ let package = Package(
     platforms: [
         .iOS(.v9),
         .tvOS(.v9),
-        .watchOS(.v2)
+        .watchOS(.v2),
+        .macOS(.v10_12),
     ],
     products: [
         // Products define the executables and libraries produced by a package, and make them visible to other packages.