nrsc5: fix license

pkgs/applications/misc/nrsc5/default.nix

···
     homepage = "https://github.com/theori-io/nrsc5";
     description = "HD-Radio decoder for RTL-SDR";
     platforms = lib.platforms.linux;
-    license = licenses.gpl3;
+    license = licenses.gpl3Plus;
     maintainers = with maintainers; [ markuskowa ];
   };
 }