pythonPackages.bcrypt: use 3.1.x for python older than 3.6

pkgs/development/python-modules/bcrypt/3_1.nix

@@ -0,0 +1,23 @@
+{ stdenv, lib, buildPythonPackage, fetchPypi
+, isPyPy, cffi, pytest, six }:
+
+buildPythonPackage rec {
+  version = "3.1.7";
+  pname = "bcrypt";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "0b0069c752ec14172c5f78208f1863d7ad6755a6fae6fe76ec2c80d13be41e42";
+  };
+
+  checkInputs = [ pytest ];
+
+  propagatedBuildInputs = [ six ] ++ lib.optional (!isPyPy) cffi;
+
+  meta = with lib; {
+    description = "Modern password hashing for your software and your servers";
+    homepage = "https://github.com/pyca/bcrypt/";
+    license = licenses.asl20;
+    maintainers = with maintainers; [ domenkozar ];
+  };
+}

pkgs/top-level/python-packages.nix

@@ -778,7 +778,10 @@ in {
 
   bcdoc = callPackage ../development/python-modules/bcdoc { };
 
-  bcrypt = callPackage ../development/python-modules/bcrypt { };
+  bcrypt = if pythonOlder "3.6" then
+    callPackage ../development/python-modules/bcrypt/3_1.nix { }
+  else
+    callPackage ../development/python-modules/bcrypt { };
 
   beaker = callPackage ../development/python-modules/beaker { };