Update ios-guide to use correct pod (#326)
Update ios-guide to use correct pod (#326)

Process to repeat warning:

* Add `pod 'Google/SignIn` to `ios/Podfile`
* `$ pod install` from command line
* Get warning `[!] Google has been deprecated`

To fix:

* Change `pod 'Google/SignIn'` to `pod 'GoogleSignIn`
devfd/react-native-google-signin,devfd/react-native-google-signin,apptailor/react-native-google-signin,apptailor/react-native-google-signin,devfd/react-native-google-signin