python3Packages.dpcontracts: migrate to pyproject

pkgs/development/python-modules/dpcontracts/default.nix

@@ -2,12 +2,13 @@
   lib,
   buildPythonPackage,
   fetchFromGitHub,
+  setuptools,
 }:
 
 buildPythonPackage {
   pname = "dpcontracts";
   version = "unstable-2018-11-20";
-  format = "setuptools";
+  pyproject = true;
 
   __structuredAttrs = true;
 
@@ -18,6 +19,10 @@ buildPythonPackage {
     hash = "sha256-FygJPXo7lZ9tlfqY6KmPJ3PLIilMGLBr3013uj9hCEs=";
   };
 
+  build-system = [
+    setuptools
+  ];
+
   # package does not have any tests
   doCheck = false;