Force another rebuild

Unfortunately, yesterday Nix got reverted to a version with broken
passAsFile implementation on some Hydra machines, so we have corrupted
files again. (E.g. http://hydra.nixos.org/build/29777678.) Forcing
another gratuitous rebuild to get rid of them.

(cherry picked from commit 75974d9220b8397c736ada76fb24eb934fa62f6c)