问无法在ruby on rails devise gem中使用sign_out

EN

<h1>Say#hello</h1>
<% if user_signed_in? %>
Hey signed in as <%= current_user.email %>.Not you? 
<%= link_to "Logout", destroy_user_session_path %>
<% else %>
Hey <%= link_to "Login", new_user_session_path %> or Hey <%= link_to "Logup", new_user_registration_path %>
<% end %>
</p>

Demo::Application.routes.draw do
devise_for :users
get "say/hello"
get "say/goodbye"
# The priority is based upon order of creation: first created -> highest priority.
# See how all your routes lay out with "rake routes".

# You can have the root of your site routed with "root"
root :to => "say#hello"
end

  Links

Hey signed in as x@gmail.com.Not you? Logout 

No route matches [GET] "/users/sign_out"

destroy_user_session_path, :method => :delete