virtualbox: 5.2.10 -> 5.2.12

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/virtualbox/versions.

These checks were done:

- built on NixOS
- ran ‘/nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12/bin/VBoxManage -h’ got 0 exit code
- ran ‘/nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12/bin/VBoxManage --help’ got 0 exit code
- ran ‘/nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12/bin/VBoxManage help’ got 0 exit code
- ran ‘/nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12/bin/VBoxBalloonCtrl -h’ got 0 exit code
- ran ‘/nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12/bin/VBoxBalloonCtrl --help’ got 0 exit code
- found 5.2.12 with grep in /nix/store/6769l9s88jlcv3qgxpjsfr1ybkq3yvvb-virtualbox-5.2.12
- directory tree listing: https://gist.github.com/f9bf852a0a8e6e0b4c44a9b68764850b