tk
/Users/shinriyo/.rbenv/versions/2.4.1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- tk (LoadError) from /Users/shinriyo/.rbenv/versions/2.4.1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb…
/Users/shinriyo/.rbenv/versions/2.4.1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- tk (LoadError) from /Users/shinriyo/.rbenv/versions/2.4.1/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb…