add -p to mkdir

pkgs/default.nix

@@ -257,7 +257,7 @@ let
     doArgotk = drv: command: drv.overrideAttrs (old:{
       buildPhase = "argotk "+command+" --verbose";
       installPhase = ''
-        mkdir $out
+        mkdir -p $out
         cp _output/* $out/
       '';
     });