Change the mention of Sonar in iOS sample app

Summary: Update the iOS sample app with flipper

Reviewed By: passy

Differential Revision: D9056882

fbshipit-source-id: f5b49fc60905c6d5ebca3da977cf966e76feffb8

iOS/Sample/AppDelegate.mm

@@ -48,7 +48,7 @@
   [_window setRootViewController: [[UINavigationController alloc] initWithRootViewController: mainViewController]];
   [_window makeKeyAndVisible];
 
-  NSLog(@"Hello from Sonar in an Objc app!");
+  NSLog(@"Hello from Flipper in an Objc app!");
   return YES;
 }