Also add nix to passthru. This makes it easier to override nix in 'nix develop', e.g.
$ nix develop
–redirect .#hydraJobs.build.x86_64-linux.nix ~/Dev/nix/outputs/out
–redirect .#hydraJobs.build.x86_64-linux.nix.dev ~/Dev/nix/outputs/dev
7HFOCQ2HMWFMHEQEH673QALNMDWCTAGA4X3DMUTL23ZIDX2BV5KQC