clutter: fix license
clutter: fix license

LGPLv2.1 or later ->
LGPLv2.1 only

Because the original sample uses LGPLv2.1 only. (FYI: Clutter itself
uses LGPLv2.1 or later.)

kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2