endlessos: update vendor for 3.8 and newer
Endless OS is now published by a new entity, Endless OS LLC. Endless OS 3.8.0 was the first release made since this transition.
(If you download the old images today, I suppose strictly speaking you are getting them from our new entity, but conceptually I think the historical vendor is accurate.)
Signed-off-by: Will Thompson wjt@endlessos.org