libmediainfo: 17.12 -> 18.03

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
/tmp/tmp.XuzpDKKIWd /home/ryantm/.cache/nixpkgs
/home/ryantm/.cache/nixpkgs
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 18.03 with grep in /nix/store/zs2mqa4yzrcy89x12hpz445b5lf8v618-libmediainfo-18.03
- directory tree listing: https://gist.github.com/647416634a701d34570d8a26d64689e7