why openjdk8?

flake.nix

@@ -68,6 +68,7 @@
         buildInputs = with pkgs; [
           android-studio
           kivy-env
+          # https://github.com/kivy/python-for-android/blob/v2020.04.29/doc/source/troubleshooting.rst#errors-related-to-java-version
           openjdk8
         ];
       };