I have the following code in my view:
<%= link_to \'Sign out\', destroy_user_session_path, method: :delete %>
Which
Do you have
//= require jquery
//= require jquery_ujs
in your application.js file?
An alternative monkey patch would be to modify the devise.rb and change the signout method to get like so
config/initializers/devise.rb
config.sign_out_via = :get
This post may shed some light: Rails 3.2 with Devise: logout link stopped working