Seeing this?

rake/rdoctask is deprecated. Use rdoc/task instead (in RDoc 2.4.2+)

Edit your Rakefile and change these lines:

require 'rake/rdoctask'
Rake::RDocTask.new(:rdoc) do |rdoc|
 ...

to look like this:

require 'rdoc/task'
RDoc::Task.new do |rdoc|
  ...

You may need to add gem 'rdoc' to your Gemfile, too. While you’re at it, you might want to add rdoc/ to your .gitignore, too