Make sure rubygems version is recent enough for CentOS6

I have the problem that I have a CentOS6 box with rubygems 1.3.7-1.el6 installed. When I want to install a gem package it complains about "invalid option: --include-dependencies".

"gem update --system" returns only "Latest version currently installed. Aborting."

There exists an update version for rubygems 1.3.7-5.el6. Unfortunately I don't know since which patchset the include-dependencies problem is fixed, but when 1.3.7-5.el6 is installed, installing packages with gem does work in CentOS6. In CentOS7 I had no problems.