pythonPackages.batchgenerators: loosen version restrictions for pillow

apply patch from MIC-DKFZ/batchgenerators#59 to
allow batchgenerators to build with pillow 7.1.2+

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

@@ -2,6 +2,7 @@
 , buildPythonPackage
 , isPy27
 , fetchFromGitHub
+, fetchpatch
 , pytest
 , unittest2
 , future
@@ -27,6 +28,13 @@ buildPythonPackage rec {
 
   };
 
+  patches = [
+    (fetchpatch {
+      url = "https://github.com/MIC-DKFZ/batchgenerators/pull/59.patch";
+      sha256 = "171b3dm40yn0wi91m9s2nq3j565s1w39jpdf1mvc03rn75i8vdp0";
+    })
+  ];
+
   propagatedBuildInputs = [
     future numpy pillow scipy scikitlearn scikitimage threadpoolctl
   ];