I had the same problem and I just found out a solution for this.
I found one related problem here:
http://techespanto.wordpress.com/2013/03/29/upgrade-ruby-version-on-mac-osx/
and it suggested I had to upgrade the ruby version on my machine. The first two commands in that link are not working, so I leave you here what I did:
Install the command line tools for mac with:
xcode-select --install
Install homebrew in your mac with:
ruby -e "$(curl -fsSL https://raw.github.com/Homebrew/homebrew/go/install)"
Install rvm with:
\curl -L https://get.rvm.io | bash -s stable --rails --autolibs=enable
List the latest ruby versions with:
rvm list known
Install the latest ruby version with:
rvm install ruby-<version>
(for me it was ruby-2.1-head
)
And that's all. Hope it works for you as well!