Update iohk-nix to hkm/update-haskell-nix branch

Author: rvl

nix/sources.json

@@ -24,15 +24,15 @@
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "iohk-nix": {
-        "branch": "master",
+        "branch": "hkm/update-haskell-nix",
         "description": "nix scripts shared across projects",
         "homepage": null,
         "owner": "input-output-hk",
         "repo": "iohk-nix",
-        "rev": "f4790863d0d4e3f9018f012ec6575432c7952a48",
-        "sha256": "0jds3j5fqcwbgpmbddrp9cxia5mxz8kw7sqsw6jcq9bq5mv1x00d",
+        "rev": "3042edd27fc0279b3246779a0657a3eda50d7d48",
+        "sha256": "0a8h2gr3kvkfck9knixidg3zknip01vdh48dycdy7chvbxnpdf39",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/iohk-nix/archive/f4790863d0d4e3f9018f012ec6575432c7952a48.tar.gz",
+        "url": "https://github.com/input-output-hk/iohk-nix/archive/3042edd27fc0279b3246779a0657a3eda50d7d48.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "niv": {