python37Packages.pyrsistent: 0.15.2 -> 0.15.4

Some tests are broken on 0.15.2 if used with pytest 5+ as discussed
in #64145. The issue is fixed in tobgu/pyrsistent#175 and released in
0.15.4.

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

@@ -20,6 +20,10 @@ buildPythonPackage rec {
 
   checkInputs = [ pytestrunner pytest_4 hypothesis ];
 
+  postPatch = ''
+    substituteInPlace setup.py --replace 'pytest<5' 'pytest'
+  '';
+
   meta = with stdenv.lib; {
     homepage = https://github.com/tobgu/pyrsistent/;
     description = "Persistent/Functional/Immutable data structures";