I've just pushed an upgrade to Zend Framework 2.1.1 to the master branch of the VuFind 2 Git repo.
This is a bug fix release, so hopefully there won't be any nasty surprises.
Just one thing to watch out for: there have been some changes to session handling, so don't upgrade the code if you're in the middle of testing with an active session. Existing sessions will be broken by this upgrade! Log out and/or clear your browser history before proceeding. If you're already using VuFind 2 in production, you might need to do some planning to work around the issue (though hopefully that's not a problem for anyone yet).