The option `services.hydra' defined in '.../hydra-network.nix' does not exist

[bjornfor]

I followed README.md and got to this step (but no further):

$ nixops deploy -d hydra
building all machine configurations...
error: The option `services.hydra' defined in `/home/bfo/forks/hydra-tutorial/hydra-network.nix' does not exist.
(use ‘--show-trace’ to show detailed location information)
error: unable to build all machine configurations

It's due to https://github.com/NixOS/hydra/commit/633724cc8aecc8fe7e586f81444bfd8d290be411 ("services.hydra -> services.hydra-dev").

[bjornfor]

Oh, there is more breakage after fixing that. For instance, the hydra module refers to gcc6. Better lock down the hydra tarball instead of always pulling from master.