Ruby » Ruby master

Merge rdoc-6.0.0.beta3.

• It version introduced did you mean? feature for ri command:
  https://github.com/ruby/rdoc/pull/533
• Removed obbsoleted ruby_token.rbb.
  [Bug #13990][ruby-core:83180]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60146 b2dd03c8-39d4-4d8f-98ff-823fe69b080e