<%= link_to "Sign Out", destroy_user_session_path,:method => :delete%>
destroy_user_session DELETE /users/logout(.:format) devise/sessions#destroy
ルーティング エラー
[GET] "/users/logout" に一致するルートはありません
devise_for :users, path_names: {sign_in: "login", sign_out: "logout"},
controllers: {omniauth_callbacks: "omniauth_callbacks"}