Use more accurate type for -supportedInterfaceOrientations

The iOS 9 headers fix the return type for -supportedInterfaceOrientations. This mutes an Xcode 7 warning.

Classes/ExplorerToolbar/FLEXExplorerViewController.m

@@ -137,10 +137,10 @@ typedef NS_ENUM(NSUInteger, FLEXExplorerMode) {
     return viewController;
 }
 
-- (NSUInteger)supportedInterfaceOrientations
+- (UIInterfaceOrientationMask)supportedInterfaceOrientations
 {
     UIViewController *viewControllerToAsk = [self viewControllerForRotationAndOrientation];
-    NSUInteger supportedOrientations = [FLEXUtility infoPlistSupportedInterfaceOrientationsMask];
+    UIInterfaceOrientationMask supportedOrientations = [FLEXUtility infoPlistSupportedInterfaceOrientationsMask];
     if (viewControllerToAsk && viewControllerToAsk != self) {
         supportedOrientations = [viewControllerToAsk supportedInterfaceOrientations];
     }