thanks you Iohannes for putting everything together and make it work
to enable os x build, i just sent an email to
support@travis-ci.com and ask them to enable OS X build for my Gem repo.
and concerning the build upload, I think the easiest is to upload on Github.
but one upload per commit would be too much.
So I think we can push an automatic Github release every time a tag is set.
Travis can do that very kindly (and thanks to Iohannes this is already set).
But daily build could be interesting too. I think we can upload at most one build per day.
FTP upload is very easy to setup in Travis, much more than ssh or something else that needs a key identification, but yes more unsecure.
Cheers
Antoine