* lib/rdoc:  Update to RDoc 4.1.0.preview.1

  RDoc 4.1.0 contains a number of enhancements including a new default
  style and accessibility support.  You can see the changelog here:

  https://github.com/rdoc/rdoc/blob/v4.1.0.preview.1/History.rdoc

* test/rdoc:  ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42971 b2dd03c8-39d4-4d8f-98ff-823fe69b080e