Build cache is always invalid

[LinusU]

For some reason, the build cache of this project is always considered invalid by Carthage 🤔

This results in this project always having to be built again when running carthage update --cache-builds:

*** Invalid cache found for OneTimePassword, rebuilding with all downstream dependencies

It seems to work for all other of my dependencies so I'm guessing that there is something special going on here 🤔