Fix OS X complaining about edge insets

Source/EdgeInsets.swift

@@ -30,12 +30,7 @@ public func EdgeInsetsMake(top: CGFloat, left: CGFloat, bottom: CGFloat, right:
 public let EdgeInsetsZero = EdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
 #else
 import AppKit
-public struct EdgeInsets {
-    public var top: CGFloat
-    public var left: CGFloat
-    public var bottom: CGFloat
-    public var right: CGFloat
-}
+public typealias EdgeInsets = NSEdgeInsets
 public func EdgeInsetsMake(top: CGFloat, left: CGFloat, bottom: CGFloat, right: CGFloat) -> EdgeInsets {
     return EdgeInsets(top: top, left: left, bottom: bottom, right: right)
 }