Bump FlipperKit version on iOS to be compatible with react-native-fli…

…pper (#28277)

Summary:
This pull request re-applies #28225, thereby reverting 4bb1794, this time bumping to FlipperKit 0.33.1 which is again compatible with iOS 9 (thanks to facebook/flipper#874)

This is the iOS counterpart of #28275

## Changelog

[iOS] [Changed] - Upgrade Flipper dependency to 0.33.1
Pull Request resolved: #28277

Test Plan:
* Bumped the version in our Flipper / RN integration test app first, that runs on 0.62-rc.5, verified everything still works there.
* CI

![Screen Shot 2020-03-10 at 12 12 46](https://user-images.githubusercontent.com/1820292/76311312-94f09f00-62c8-11ea-81db-ced6d16e096b.png)

Reviewed By: mweststrate

Differential Revision: D20369106

Pulled By: TheSavior

fbshipit-source-id: dfeb0446e7f29684a266eca5d0e29ac42cef2ef3

scripts/react_native_pods.rb

@@ -57,7 +57,7 @@ def use_react_native! (options={})
   end
 end
 
-def use_flipper!(version = '~> 0.32.2')
+def use_flipper!(version = '~> 0.33.1')
   pod 'FlipperKit', version, :configuration => 'Debug'
   pod 'FlipperKit/FlipperKitLayoutPlugin', version, :configuration => 'Debug'
   pod 'FlipperKit/SKIOSNetworkPlugin', version, :configuration => 'Debug'