Some time ago the data structure for maintainer descriptions in nixpkgs changed from a simple attr set with maintainer emails as values to an attribute set where the maintainer' nick is associated to an attribute set with email, GitHub handle and full name.

Hydra can either parse a Nix list or fetches shortName from the associated attribute set (which is used for meta.licenses as each value in it contains a shortName). This behavior needs to be replicated for maintainers to retrieve the emails for hydra-notify.

This change is backwards-compatible since queryMetaStrings is still able to understand lists, so old versions of nixpkgs or packages using the old maintainer data structure remain usable.