Eu descobri uma solução alternativa para isso:
apt-get update
apt-get install -y automake bison build-essential git-core libffi-dev libreadline6-dev libgdbm3 libgdbm-dev libncurses5-dev libssl-dev libtool libyaml-dev vim zlib1g-dev
[ -e /opt/ruby-build ] || {
git clone git://github.com/sstephenson/ruby-build.git /opt/ruby-build
/opt/ruby-build/bin/ruby-build 2.2.0 /opt/ruby-2.2.0
echo PATH="/opt/ruby-2.2.0/bin:\$PATH" >> /etc/profile
PATH="/opt/ruby-2.2.0/bin:$PATH"
}