predeclare the method so that there is no warning

Author: Igor Makarov

Sources/UIViewController+AnyPromise.m

@@ -13,7 +13,9 @@ @interface PMKGenericDelegate : NSObject <UINavigationControllerDelegate> {
 + (instancetype)delegateWithPromise:(AnyPromise **)promise;
 @end
 
-
+@interface UIViewController ()
+- (AnyPromise*) promise;
+@end
 
 @implementation UIViewController (PromiseKit)