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

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

<details><summary>Version release notes (from GitHub)</summary>
## Lynis 2.6.6 (2018-07-06)

### Improvements
* New format of changelog (https://keepachangelog.com/en/1.0.0/)
* KRNL-5830 - improved log text about running kernel version

### Fixed
* Under some condition no hostid2 value was reported
* Solved 'extra operand' issue with tr command</details>

These checks were done:

- built on NixOS
- /nix/store/ds1yfrg5q01q8j64yggb3p5ib5crg26c-lynis-2.6.6/bin/lynis passed the binary check.
- /nix/store/ds1yfrg5q01q8j64yggb3p5ib5crg26c-lynis-2.6.6/bin/.lynis-wrapped 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 2.6.6 with grep in /nix/store/ds1yfrg5q01q8j64yggb3p5ib5crg26c-lynis-2.6.6
- directory tree listing: https://gist.github.com/1539c4e988dbc040136beb3577edd526
- du listing: https://gist.github.com/149b0c5b68a57473edf905b2bb6c03a8

lynis: 2.6.5 -> 2.6.6