python27Packages.youtube-dl: 2018.05.09 -> 2018.05.18

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

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

These checks were done:

- built on NixOS
- /nix/store/xdrcf96p90hk4cdpwjcafvqz9dhpab0p-youtube-dl-2018.05.18/bin/.youtube-dl-wrapped passed the binary check.
- /nix/store/xdrcf96p90hk4cdpwjcafvqz9dhpab0p-youtube-dl-2018.05.18/bin/youtube-dl passed the binary check.
- 2 of 2 passed binary check by having a zero exit code.
- 2 of 2 passed binary check by having the new version present in output.
- found 2018.05.18 with grep in /nix/store/xdrcf96p90hk4cdpwjcafvqz9dhpab0p-youtube-dl-2018.05.18
- directory tree listing: https://gist.github.com/d85bbc7695f5c7236d2de010c6381975
- du listing: https://gist.github.com/c5ad848ac823c72e329d20063defbc67