python{2,3}Packages.pytest-repeat: fix build

Test suite and build environment had several issues with Pytest >3.6
which can be fixed by applying the (yet unreleased) upstream patch from
f94b6940e3.patch

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

@@ -3,6 +3,7 @@
 , fetchPypi
 , setuptools_scm
 , pytest
+, fetchpatch
 }:
 
 buildPythonPackage rec {
@@ -14,6 +15,15 @@ buildPythonPackage rec {
     sha256 = "0axbrpqal3cqw9zq6dakdbg49pnf5gvyvq6yn93hp1ayc7fnhzk3";
   };
 
+  # fixes support for pytest >3.6. Should be droppable during the
+  # next bump.
+  patches = [
+    (fetchpatch {
+      url = https://github.com/pytest-dev/pytest-repeat/commit/f94b6940e3651b7593aca5a7a987eb56abe04cb1.patch;
+      sha256 = "00da1gmpq9pslcmm8pw93jcbp8j2zymzqdsm6jq3xinkvjpsbmny";
+    })
+  ];
+
   buildInputs = [ setuptools_scm pytest ];
 
   checkPhase = ''