geant4: fix eval

Regression from 66e44425c6dfecbea68a5d6dc221ccd56561d4f1

pkgs/development/libraries/physics/geant4/datasets.nix

···
-{ stdenv, fetchurl, geant_version }:
+{ lib, stdenv, fetchurl, geant_version }:
 
 let
   mkDataset = { name, version, sha256, envvar }:

pkgs/development/libraries/physics/geant4/default.nix

···
 
   passthru = {
     data = import ./datasets.nix {
-          inherit stdenv fetchurl;
+          inherit lib stdenv fetchurl;
           geant_version = version;
       };