atlantis: fix build on darwin

pkgs/applications/networking/cluster/atlantis/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, buildGoModule, fetchFromGitHub }:
+{ stdenv, buildGoModule, fetchFromGitHub, Security }:
 
 buildGoModule rec {
   pname = "atlantis";
@@ -15,6 +15,8 @@ buildGoModule rec {
 
   subPackages = [ "." ];
 
+  buildInputs = stdenv.lib.optionals stdenv.isDarwin [ Security ];
+
   meta = with stdenv.lib; {
     homepage = "https://github.com/runatlantis/atlantis";
     description = "Terraform Pull Request Automation";