I don't use tool/sync_default_gem.rb because the last sync was incomplete.

Co-authored-by: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>
Co-authored-by: sinisterchipmunk <sinisterchipmunk@gmail.com>
Co-authored-by: Sutou Kouhei <kou@clear-code.com>