OSX: issue updater

Issue generated from Tuleap's migration script. Originally submitted by: Alexandre Lision (alision)

Seen in log:

App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file.

We use this URL to check for client updates: http://gpl.savoirfairelinux.net/ring-download/mac\_osx/sparkle-ring.xml

It should be https.

It is not always reproductible, I've been capable to update a client with this URL. It may be enforced recently by newer versions of OSX. We should better fix it now.