urukul: build with nixos 19.09

hydra/artiq.json

@@ -10,7 +10,7 @@
     "emailoverride": "",
     "keepnr": 10,
     "inputs": {
-        "nixpkgs": { "type": "git", "value": "git://github.com/NixOS/nixpkgs-channels nixos-19.03", "emailresponsible": false },
+        "nixpkgs": { "type": "git", "value": "git://github.com/NixOS/nixpkgs-channels nixos-19.09", "emailresponsible": false },
         "nixScripts": { "type": "git", "value": "https://git.m-labs.hk/M-Labs/nix-scripts.git", "emailresponsible": false }
     }
 }