Add nkf to gemspec

[kapitoshka438]

After upgrading to Ruby 3.3.0 running bundle install for a single Gemfile which only contains Fastlane gem shows this warning

{PROJECT_ROOT}/vendor/bundle/ruby/3.3.0/gems/CFPropertyList-3.0.6/lib/cfpropertylist/rbCFPropertyList.rb:3: warning: kconv is found in nkf, which will no longer be part of the default gems since Ruby 3.4.0. Add nkf to your Gemfile or gemspec. Also contact author of CFPropertyList-3.0.6 to add nkf into its gemspec.

[ckruse]

Should be fixed now, at least I no longer can reproduce it on my dev machine. Can you confirm?

[kapitoshka438]

After taking a look on your changes I can assume that it will work for Ruby 3.4.0 (which is not released yet) but it won't fix the Ruby 3.3.0 warning. But it's probably fine.

[ckruse]

Sorry, I remembered it wrong. You are right, should be specified for 3.3, too.

[ckruse]

Ok, I pushed a new version to rubygems. Thank you for your report! ❤️