Don't add trailing newline to keyfile

[StillerHarpo]

pass will add an trailing newline which renders luks login via prompt useless

[phaer]

Nice catch, but as that's mostly an example I think the better solution might be to add a check or just strip trailing newlines for any keyFiles? (i.e. #161 (comment))

[StillerHarpo]

I'm going to fix this in disko directly with nix-community/disko#323. So we can close this without merging after that got merged

[phaer]

Thanks, has been merged in disko!