Update ghc-artefact-nix

Fixing #39 with https://github.com/mpickering/ghc-artefact-nix/pull/14.

ci/ghc-from-artifact.nix

@@ -7,14 +7,7 @@ in
 let
   nixpkgsSrc = sources.nixpkgs;
   ghc-artefact-nix =
-    let
-      src = nixpkgs.fetchFromGitHub {
-        owner = "mpickering";
-        repo = "ghc-artefact-nix";
-        rev = "5da00a2f9411f15a7e0cbacc0ad94ff4ffa195d7";
-        sha256 = "sha256:1ab2hc893vlsclddqyvw3yrhg33sn7pjckl2v8yi67d2jwc9zygn";
-      };
-    in import src {
+    import sources.ghc-artefact-nix {
       url = ghcTarball;
       nixpkgsSrc = sources.nixpkgs;
     };

ci/nix/sources.json

@@ -11,6 +11,18 @@
         "url": "https://github.com/commercialhaskell/all-cabal-hashes/archive/3a406043fb5586e6016440b65759b10b036cdb4f.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "ghc-artefact-nix": {
+        "branch": "master",
+        "description": "Create environments with GHC HEAD artefacts",
+        "homepage": null,
+        "owner": "mpickering",
+        "repo": "ghc-artefact-nix",
+        "rev": "04663ad09ceb0306156e44cb76625cf0d34db3b1",
+        "sha256": "0a6ji9jbxj0vnszjf6wgvx2jbrsb6skjgb9r92gc7bv7hg0fszqv",
+        "type": "tarball",
+        "url": "https://github.com/mpickering/ghc-artefact-nix/archive/04663ad09ceb0306156e44cb76625cf0d34db3b1.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "hackage-security": {
         "branch": "master",
         "description": "Hackage security framework based on TUF (The Update Framework)",