Merge pull request sparkle-project#2 from ksuther/ui-separation-and-xpc

Fixed retain cycle between SPUBasicUpdateDriver and SUAppcastDriver

Sparkle/SUAppcastDriver.m

@@ -27,7 +27,7 @@ @interface SUAppcastDriver ()
 @property (nullable, nonatomic, readonly, weak) id updater;
 @property (nullable, nonatomic, readonly, weak) id <SPUUpdaterDelegate> updaterDelegate;
 @property (nullable, nonatomic) SUAppcastItem *nonDeltaUpdateItem;
-@property (nullable, nonatomic, readonly) id <SUAppcastDriverDelegate> delegate;
+@property (nullable, nonatomic, readonly, weak) id <SUAppcastDriverDelegate> delegate;
 
 @end