Nix expr: fix derivation import in overlay output

Author: SignalWalker

flake.nix

@@ -49,8 +49,8 @@
         # filter derivations to only include `emuhawk` and `discohawk` ones (i.e. excluding `bizhawkAssemblies`)
         std.filterAttrs (name: pkg: (std.hasPrefix "emuhawk" name) || (std.hasPrefix "discohawk" name)) (
           # import `default.nix` with the overlayed package set
-          # (i don't know the circumstances under which `prev` wouldn't have a `system` attribute, but we may as well account for it)
-          importDefaultDerivationsWith (prev.system or "") prev
+          # (i don't know the circumstances under which `final` wouldn't have a `system` attribute, but we may as well account for it)
+          importDefaultDerivationsWith (final.system or "") final
         );
       apps =
         let