Fix for nixops

pkgs/default.nix

@@ -22,5 +22,12 @@ self: super:
   ripmime = super.ripmime.override {
     stdenv = super.overrideCC super.stdenv super.gcc6;
   };
+  nixops = super.nixops.overrideDerivation (
+  old: {
+    patchPhase = ''
+        substituteInPlace nix/eval-machine-info.nix \
+            --replace 'system.nixosVersion' 'system.nixos.version'
+    '';
+  });
 }