python3Packages.emv: relax pycountry constraint

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

···
       --replace '"argparse==1.4.0",' "" \
       --replace "click==7.1.2" "click" \
       --replace "pyscard==2.0.0" "pyscard" \
+      --replace "pycountry==20.7.3" "pycountry" \
       --replace "terminaltables==3.1.0" "terminaltables"
   '';