translating source/ko/active_support_core_extensions.md and updated rails_guides/markdown/rederer.rb
Merge pull request #21 from hschoidr/master

updated rails_guides/markdown/renderer.rb
translating guides/source/ko/active_support_core_extensions.md
Merge pull request #22 from hschoidr/master

translating guides/source/ko/active_support_core_extensions.md, updated