gtk2: fix Gtk::AboutDialog#show("wrap_license" => ...)

[ruby-gnome2-devel-ja]

Patch by Hiroyuki Ito. Thanks!!!
gtk3: fix Gtk::AboutDialog#show("wrap_license" => ...)

[ruby-gnome2-devel-ja]

Patch by Hiroyuki Ito. Thanks!!!
gtk3: support Gtk::AboutDialog#show("license_type" => ...)

[ruby-gnome2-devel-ja]

Patch by Hiroyuki Ito. Thanks!!!