* README.EXT.ja: [DOC] Fix typo by @utenmiki [Fixes GH-534] [ci skip]
  https://github.com/ruby/ruby/pull/534


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44992 b2dd03c8-39d4-4d8f-98ff-823fe69b080e