[ReactNative] Fix alert out of main thread

Summary:
@public

I've added an alert to notify when the profile has been generated, but it was
being created out of the main thread.

Test Plan:
Launch the UIExplorer, start and stop profiling, an alert should show up, and
everything should just keep working as expected.

React/Base/RCTBridge.m

@@ -1530,11 +1530,13 @@ RCT_INNER_BRIDGE_ONLY(_invokeAndProcessModule:(__unused NSString *)module
        if (error) {
          RCTLogError(@"%@", error.localizedDescription);
        } else {
-         [[[UIAlertView alloc] initWithTitle:@"Profile"
-                                     message:@"The profile has been generated, check the dev server log for instructions."
-                                    delegate:nil
-                           cancelButtonTitle:@"OK"
-                           otherButtonTitles:nil] show];
+         dispatch_async(dispatch_get_main_queue(), ^{
+           [[[UIAlertView alloc] initWithTitle:@"Profile"
+                                       message:@"The profile has been generated, check the dev server log for instructions."
+                                      delegate:nil
+                             cancelButtonTitle:@"OK"
+                             otherButtonTitles:nil] show];
+         });
        }
      }];