sigil: update license

Author: Prince213

pkgs/by-name/si/sigil/package.nix

@@ -64,7 +64,7 @@ stdenv.mkDerivation rec {
   meta = {
     description = "Free, open source, multi-platform ebook (ePub) editor";
     homepage = "https://github.com/Sigil-Ebook/Sigil/";
-    license = lib.licenses.gpl3;
+    license = lib.licenses.gpl3Plus;
     maintainers = with lib.maintainers; [ prince213 ];
     platforms = with lib.platforms; linux ++ darwin;
     mainProgram = "sigil";