[ruby/date] Use Gemfile instead of Gem::Specification#add_development_dependency.
https://github.com/ruby/date/commit/13c94362c2
[ruby/date] Use Gemfile instead of Gem::Specification#add_development_dependency.
https://github.com/ruby/date/commit/13c94362c2