Swift 4.2 support

Sources/DataStack+Observing.swift

@@ -2,7 +2,7 @@
 //  DataStack+Observing.swift
 //  CoreStore
 //
-//  Copyright © 2015 John Rommel Estropia
+//  Copyright © 2018 John Rommel Estropia
 //
 //  Permission is hereby granted, free of charge, to any person obtaining a copy
 //  of this software and associated documentation files (the "Software"), to deal
@@ -29,7 +29,7 @@ import CoreData
 
 // MARK: - DataStack
 
-@available(OSX 10.12, *)
+@available(macOS 10.12, *)
 public extension DataStack {
     
     /**