macOS compatible

Sources/Kingfisher.swift

@@ -30,12 +30,14 @@ import ImageIO
 #if os(macOS)
     import AppKit
     public typealias Image = NSImage
+    public typealias View = NSView
     public typealias Color = NSColor
     public typealias ImageView = NSImageView
     typealias Button = NSButton
 #else
     import UIKit
     public typealias Image = UIImage
+    public typealias View = UIView
     public typealias Color = UIColor
     #if !os(watchOS)
     public typealias ImageView = UIImageView

Sources/Placeholder.swift

@@ -42,7 +42,7 @@ extension Placeholder where Self: Image {
 
 extension Image: Placeholder {}
 
-extension Placeholder where Self: UIView {
+extension Placeholder where Self: View {
     public func add(to imageView: ImageView) {
         imageView.addSubview(self)