Motivation for this change

NixOS wouldn't build because the nginx config checker fails.

Location without a trailing slash "could allow an attacker to read file
stored outside the target folder.", source:
https://github.com/yandex/gixy/blob/master/docs/en/plugins/aliastraversal.md

Shouldn't change the behaviour according to
https://serverfault.com/questions/607615/using-trailing-slashes-in-nginx-configuration/607731#607731

cc @peterhoeg @aanderse

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

Can be tested with this minimal config:

  services.zoneminder = {
    enable = true;
    database = {
      createLocally = true;
      username = "zoneminder";
    };
  };