clightning: fix build

pkgs/clightning-mistune-workaround/default.nix

@@ -0,0 +1,12 @@
+{ clightning, python3 }:
+
+clightning.override {
+  python3 = python3.override {
+    packageOverrides = self: super: {
+      mistune = self.callPackage ./mistune.nix {
+        version = "0.8.4";
+        sha256 = "59a3429db53c50b5c6bcc8a07f8848cb00d7dc8bdb431a4ab41920d201d4756e";
+      };
+    };
+  };
+}

pkgs/clightning-mistune-workaround/mistune.nix

@@ -0,0 +1,27 @@
+{ lib
+, buildPythonPackage
+, fetchPypi
+, nose
+, version
+, sha256
+, format ? "setuptools"
+, extraMeta ? {}
+}:
+
+buildPythonPackage rec {
+  inherit version format;
+  pname = "mistune";
+
+  src = fetchPypi {
+    inherit pname version sha256;
+  };
+
+  buildInputs = [ nose ];
+  pythonImportsCheck = [ "mistune" ];
+
+  meta = with lib; {
+    description = "The fastest markdown parser in pure Python";
+    homepage = "https://github.com/lepture/mistune";
+    license = licenses.bsd3;
+  } // extraMeta;
+}