fix typo.
2.1.0-preview1 -> 2.1.0-preview2
Merge pull request #397 from muryoimpl/fix-typo-news-2013-11-22-ruby-2-1-0-preview2-is-released

Fix typo in ja/news/_post/2013-11-22-ruby-2-1-0-preview2-is-released.md.