* lib/rubygems: Update to RubyGems 2.0.6. [ruby-core:56160]
  [Backport #8682]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@42170 b2dd03c8-39d4-4d8f-98ff-823fe69b080e