* lib/rubygems:  Update to RubyGems master 2abce58.  Changes:

  Fixed documentation generation when sdoc and json are installed as
  gems.

  Added some missing documentation.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43317 b2dd03c8-39d4-4d8f-98ff-823fe69b080e