Use the right key for the image thumbnail dictionaries in the URL

resources struct.

Fixes rdar://27556178

Author: parkera

stdlib/public/SDK/AppKit/AppKit_FoundationExtensions.swift

@@ -75,8 +75,8 @@ public extension URLResourceValues {
 
     /// Returns a dictionary of NSImage objects keyed by size.
     @available(OSX 10.10, *)
-    public var thumbnailDictionary : [URLThumbnailSizeKey : NSImage]? {
-        return allValues[URLResourceKey.thumbnailDictionaryKey] as? [URLThumbnailSizeKey : NSImage]
+    public var thumbnailDictionary : [URLThumbnailDictionaryItem : NSImage]? {
+        return allValues[URLResourceKey.thumbnailDictionaryKey] as? [URLThumbnailDictionaryItem : NSImage]
     }
 
 }

stdlib/public/SDK/UIKit/UIKit_FoundationExtensions.swift.gyb

@@ -80,8 +80,8 @@ public extension URLResourceValues {
 
     /// Returns a dictionary of UIImage objects keyed by size.
     @available(iOS 8.0, *)
-    public var thumbnailDictionary : [URLThumbnailSizeKey : UIImage]? {
-        return allValues[URLResourceKey.thumbnailDictionaryKey] as? [URLThumbnailSizeKey : UIImage]
+    public var thumbnailDictionary : [URLThumbnailDictionaryItem : UIImage]? {
+        return allValues[URLResourceKey.thumbnailDictionaryKey] as? [URLThumbnailDictionaryItem : UIImage]
     }
 }