fix(app, ios): formally note cocoapods v1.10+ requirement in podspec

cocoapods has needed a minimum version of 1.10 for quite some time, so this
is not actually a breaking change, the breaking change was before v10 I think,
this just makes it much more obvious with good messaging, versus previous subtle
error behavior

packages/app/RNFBApp.podspec

@@ -16,6 +16,7 @@ Pod::Spec.new do |s|
   s.source              = { :git => "https://github.com/invertase/react-native-firebase.git", :tag => "v#{s.version}" }
   s.social_media_url    = 'http://twitter.com/invertaseio'
   s.ios.deployment_target = "10.0"
+  s.cocoapods_version   = '>= 1.10.0'
   s.source_files        = "ios/**/*.{h,m}"
 
   # React Native dependencies