* lib/rubygems:  Update to RubyGems master 42543b6.  Changes:

  Fix `gem update` for gems with multiple platforms.

* test/rubygems:  ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43359 b2dd03c8-39d4-4d8f-98ff-823fe69b080e