Use cabal-version 2.4 (#141)

On cabal-install-2.4, using cabal-version 2.2 means that a lot of
extra-source-files don't get detected.

dhall-to-cabal.cabal

@@ -1,4 +1,4 @@
-cabal-version: 2.2
+cabal-version: 2.4
 -- * * * * * * * * * * * * WARNING * * * * * * * * * * * *
 -- This file has been AUTO-GENERATED by dhall-to-cabal.
 --

dhall-to-cabal.dhall

@@ -75,7 +75,9 @@ in  let warning-options =
 
 in    prelude.utils.GitHub-project
       { owner = "ocharles", repo = "dhall-to-cabal" }
-    ⫽ { synopsis =
+    ⫽ { cabal-version =
+          v "2.4"
+      , synopsis =
           "Compile Dhall expressions to Cabal files"
       , description =
           ''

dhall-to-cabal.nix

@@ -0,0 +1,27 @@
+{ mkDerivation, base, bytestring, Cabal, containers, contravariant
+, dhall, Diff, directory, filepath, hashable, microlens
+, optparse-applicative, prettyprinter, stdenv, tasty, tasty-golden
+, tasty-hunit, text, transformers, vector
+}:
+mkDerivation {
+  pname = "dhall-to-cabal";
+  version = "1.3.1.0";
+  src = ./.;
+  isLibrary = true;
+  isExecutable = true;
+  libraryHaskellDepends = [
+    base bytestring Cabal containers contravariant dhall hashable text
+    transformers vector
+  ];
+  executableHaskellDepends = [
+    base bytestring Cabal dhall directory filepath microlens
+    optparse-applicative prettyprinter text transformers
+  ];
+  testHaskellDepends = [
+    base bytestring Cabal dhall Diff filepath microlens prettyprinter
+    tasty tasty-golden tasty-hunit text
+  ];
+  homepage = "https://github.com/ocharles/dhall-to-cabal";
+  description = "Compile Dhall expressions to Cabal files";
+  license = stdenv.lib.licenses.mit;
+}

release.nix

@@ -39,20 +39,7 @@ let
 
           insert-ordered-containers = self.callPackage ./insert-ordered-containers.nix {};
 
-          dhall-to-cabal =
-            self.callCabal2nix
-              "dhall-to-cabal"
-              ( import
-                  ./cabal-sdist.nix
-                  { inherit ( pkgs.stdenv ) mkDerivation;
-                    inherit ( pkgs ) cabal-install;
-                    ghc = self.ghcWithPackages (hs: [
-                      (hs.callPackage ./cabal.nix {})
-                    ]);
-                  }
-                  ./.
-              )
-              {};
+          dhall-to-cabal = self.callPackage ./dhall-to-cabal.nix {};
         };
       };
     };