mkdocs: 0.16.3 -> 0.17.2

Semi-automatic update. These checks were performed:

- built on NixOS
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/.mkdocs-wrapped -h` got 0 exit code
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/.mkdocs-wrapped --help` got 0 exit code
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/.mkdocs-wrapped -V` and found version 0.17.2
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/.mkdocs-wrapped --version` and found version 0.17.2
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/mkdocs -h` got 0 exit code
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/mkdocs --help` got 0 exit code
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/mkdocs -V` and found version 0.17.2
- ran `/nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2/bin/mkdocs --version` and found version 0.17.2
- found 0.17.2 with grep in /nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2
- found 0.17.2 in filename of file in /nix/store/hndrgmyp176jgfgy4iyf0wdf21hhbdwv-mkdocs-0.17.2