pytest-black: patch black dependency

This change is pending upstream in #29, but it is stale.

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

@@ -14,7 +14,7 @@ buildPythonPackage rec {
     sha256 = "0f8mr0yzj78q1dx7v6ggbgfir2wv0n5z2shfbbvfdq7910xbgvf2";
   };
 
-  buildInputs = [ setuptools_scm ];
+  nativeBuildInputs = [ setuptools_scm ];
   checkInputs =  [ pytest glibcLocales ];
 
   # Necessary for the tests to pass on Darwin with sandbox enabled.

pkgs/development/python-modules/pytest-black/black-version.patch

@@ -0,0 +1,13 @@
+diff --git a/setup.py b/setup.py
+index 5c9ce5f..84b148a 100644
+--- a/setup.py
++++ b/setup.py
+@@ -26,6 +26,6 @@ setup(
+     python_requires=">=2.7",
+     install_requires=[
+         "pytest>=3.5.0",
+-        'black==19.3b0; python_version >= "3.6"',
++        'black; python_version >= "3.6"',
+         "toml",
+     ],
+     use_scm_version=True,

pkgs/development/python-modules/pytest-black/default.nix

@@ -14,6 +14,7 @@ buildPythonPackage rec {
     sha256 = "03gwwy1h3qnfh6vpfhgsa5ag53a9sw1g42sc2s8a2hilwb7yrfvm";
   };
 
+  patches = [ ./black-version.patch ];
   nativeBuildInputs = [ setuptools_scm ];
 
   propagatedBuildInputs = [ black pytest toml ];