opensc: fix ill-defined escape sequence in version regex

Nix warns about \. being an ill-defined escape. Use \\. to properly
escape the backslash so the regex still matches a literal dot.

pkgs/by-name/op/opensc/package.nix

@@ -67,7 +67,7 @@ stdenv.mkDerivation (finalAttrs: {
     "completiondir=$(out)/etc"
   ];
 
-  passthru.updateScript = nix-update-script { extraArgs = [ "--version-regex=^([0-9\.]+)$" ]; };
+  passthru.updateScript = nix-update-script { extraArgs = [ "--version-regex=^([0-9\\.]+)$" ]; };
 
   meta = {
     description = "Set of libraries and utilities to access smart cards";