Update nixos-20.03

Also remove nixos-unstable testing

nix/sources.json

@@ -5,22 +5,10 @@
         "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "NixOS",
         "repo": "nixpkgs-channels",
-        "rev": "29eddfc36d720dcc4822581175217543b387b1e8",
+        "rev": "aaa66d8d887c73f643246ac1a684fcb1521543b8",
-        "sha256": "1gqv2m7plkladd3va664xyqb962pqs4pizzibvkm1nh0f4rfpxvy",
+        "sha256": "0qvrhc7hv8h4yqa4jh64y6v5j3nza53ivkbq6j72g434c3yp2h50",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/29eddfc36d720dcc4822581175217543b387b1e8.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs-channels/archive/aaa66d8d887c73f643246ac1a684fcb1521543b8.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "nixpkgs-unstable": {
-        "branch": "nixos-unstable",
-        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
-        "homepage": "https://github.com/NixOS/nixpkgs",
-        "owner": "NixOS",
-        "repo": "nixpkgs-channels",
-        "rev": "fce7562cf46727fdaf801b232116bc9ce0512049",
-        "sha256": "14rvi69ji61x3z88vbn17rg5vxrnw2wbnanxb7y0qzyqrj7spapx",
-        "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/fce7562cf46727fdaf801b232116bc9ce0512049.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

tests/default.nix

@@ -28,7 +28,6 @@ let
 
   releaseNames = [
     "nixpkgs-20.03"
-    "nixpkgs-unstable"
   ];
 
   testNames = [