requests-aws4auth: only disable tests on python >= 3

pkgs/development/python-modules/requests-aws4auth/default.nix

···
-{ lib, buildPythonPackage, fetchPypi, requests }:
+{ lib, buildPythonPackage, fetchPypi, fetchzip, isPy3k, requests }:
+with lib;
 buildPythonPackage rec {
   pname = "requests-aws4auth";
   version = "0.9";
···
     sha256 = "0g52a1pm53aqkc9qb5q1m918c1qy6q47c1qz63p5ilynfbs3m5y9";
   };
 
+  postPatch = optionalString isPy3k ''
+    sed "s/path_encoding_style/'path_encoding_style'/" \
+      -i requests_aws4auth/service_parameters.py
+  '';
+
   propagatedBuildInputs = [ requests ];
 
-  doCheck = false;
+  # The test fail on Python >= 3 because of module import errors.
+  doCheck = !isPy3k;
 
-  meta = with lib; {
+  meta = {
     description = "Amazon Web Services version 4 authentication for the Python Requests library.";
     homepage = https://github.com/sam-washington/requests-aws4auth;
     license = licenses.mit;