chore: Update Podfile snippet to specify iOS version.
chore: Update Podfile snippet to specify iOS version.

Change-Id: Ic860b2b81da3b96896aa66d5a27efeae68f0e481

googlemaps/maps-sdk-for-ios-samples,googlemaps/maps-sdk-for-ios-samples,googlemaps/maps-sdk-for-ios-samples,googlemaps/maps-sdk-for-ios-samples