hetzner-nixops-installer: Build on Hydra.

This is in order to prepare for fetching the build output from the corresponding
target machine to even further speed up deployment.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/tools/misc/hetzner-nixops-installer/default.nix

@@ -102,6 +102,7 @@ in stdenv.mkDerivation {
                        (remember, we're on a non-NixOS system here), together
                        with the partitioner.
     '';
+    platforms = stdenv.lib.platforms.all;
     maintainers = [ stdenv.lib.maintainers.aszlig ];
   };
 }