Apply suggestions from code review

pkgs/development/libraries/luabind/default.nix

···
   src = fetchFromGitHub {
     owner = "luabind";
     repo = "luabind";
-    rev = "v${version}";
+    rev = version;
     sha256 = "sha256-sK1ca2Oj9yXdmxyXeDO3k8YZ1g+HxIXLhvdTWdPDdag=";
   };
 

pkgs/development/libraries/nco/default.nix

···
   src = fetchFromGitHub {
     owner = "nco";
     repo = "nco";
-    rev = "${version}";
+    rev = version;
     sha256 = "sha256-KrFRBlD3z/sjKIvxmE0s/xCILQmESecilnlUGzDDICw=";
   };