Files tab crash when README is in textile

When the README file is in textile format, the page of Files tab crashed with the following log messages:

Started GET "/hanwentao/oh-my-zsh/tree/master" for x.x.x.x at 2014-07-11 10:39:43 +0800
Processing by Projects::TreeController#show as HTML
  Parameters: {"project_id"=>"hanwentao/oh-my-zsh", "id"=>"master"}
Completed 500 Internal Server Error in 43ms

LoadError (cannot load such file -- redcloth):
  app/helpers/application_helper.rb:224:in `render_markup'
  app/views/projects/tree/_readme.html.haml:13:in `_app_views_projects_tree__readme_html_haml___2462924999633757807_107879200'
  app/views/projects/tree/_tree.html.haml:45:in `_app_views_projects_tree__tree_html_haml___2851900532322436067_106877160'
  app/views/projects/tree/show.html.haml:9:in `_app_views_projects_tree_show_html_haml__2514478862087347091_106300100'
  app/controllers/projects/tree_controller.rb:6:in `show'