[SE-0112] Fix an iOS-only test for NSError bridging.

Author: DougGregor

test/1_stdlib/AssetsLibrary.swift

@@ -11,6 +11,6 @@ let library = ALAssetsLibrary()
 library.enumerateGroupsWithTypes(ALAssetsGroupAll,
   usingBlock: {(group: ALAssetsGroup?, stop: UnsafeMutablePointer<ObjCBool>?) -> Void in
                 print("Swift usingBlock")},
-  failureBlock: {(error: NSError?) -> Void in
+  failureBlock: {(error: Error?) -> Void in
                   print("Swift failureBlock")})