Revert r42938 "* lib/rubygems:  Update to RubyGems 2.1.3"

It breaks build.
http://u64.rubyci.org/~chkbuild/ruby-trunk/log/20130913T200302Z.diff.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42941 b2dd03c8-39d4-4d8f-98ff-823fe69b080e