krunner-symbols: fix license

pkgs/desktops/plasma-5/3rdparty/addons/krunner-symbols.nix

···
   meta = with lib; {
     description = "A little krunner plugin (Plasma 5) to retrieve unicode symbols, or any other string, based on a corresponding keyword";
     homepage = "https://github.com/domschrei/krunner-symbols";
-    license = licenses.gpl3Only;
+    license = licenses.gpl3Plus;
     maintainers = with maintainers; [ hqurve ];
     platforms = platforms.linux;
   };