Semi-automatic update. These checks were performed:
- built on NixOS
- ran `/nix/store/cqjd4b5av6rrmmz9qvagqgq2vqwi5mmi-qgis-2.18.16/bin/qgis_bench -h` got 0 exit code
- found 2.18.16 with grep in /nix/store/cqjd4b5av6rrmmz9qvagqgq2vqwi5mmi-qgis-2.18.16
cc "@viric"