Motivation for this change

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.

This version contains a number of important fixes and is the current stable release.

Making the derivation overridable allows future Docker releases to be tested using a NixOS overlay similar to this:

self: super:

{
  docker = super.docker.override {
    version = "18.09.5";
    rev = "e8ff056dbcfadaeca12a5f508b0cec281126c01d";
    sha256 = "16nd9vg2286m6v47fjq2zicmfvi8vwiwn24yylxia8b9mk417kdb";
    runcRev = "2b18fe1d885ee5083ef9f0838fee39b62d653e30";
    runcSha256 = "0g0d9mh5fcvsjgddiyw98ph5zpz5ivlwy89m45jxwbzkxb21gy7w";
    containerdRev = "bb71b10fd8f58240ca47fbb579b9d1028eea7c84";
    containerdSha256 = "0npbzixf3c0jvzm159vygvkydrr8h36c9sq50yv0mdinrys2bvg0";
    tiniRev = "fec3683b971d9c3ef73f284f176672c44b448662";
    tiniSha256 = "1h20i3wwlbd8x4jr2gz68hgklh0lb0jj7y5xk1wvr8y58fip1rdn";
  };
}