nixos: add StateDirectory for fprintd

nixos/modules/services/security/fprintd.nix

@@ -50,6 +50,13 @@ in
 
     systemd.packages = [ cfg.package ];
 
+
+    # The upstream unit does not use StateDirectory, and will
+    # fail if the directory it needs is not present. Should be
+    # fixed when https://gitlab.freedesktop.org/libfprint/fprintd/merge_requests/5
+    # is merged.
+    systemd.services.fprintd.serviceConfig.StateDirectory = "fprint";
+
   };
 
 }