swift version is still 4.1 on CocoaPods website

[iago849]

Please look and update here
https://github.com/CocoaPods/Specs/blob/master/Specs/d/5/2/CodableFirebase/0.2.1/CodableFirebase.podspec.json
without direct link to git noone can install latest version by simply
pod 'CodableFirebase'