Fix sign out link

The correct HTML attribute to send a DELETE request would be
`data-turbo-method`, but then it still fails with JS turned off, which
is unnecessary.

fixes #61

app/views/shared/_header_account.html.erb

@@ -1,6 +1,6 @@
 <% if user_signed_in? %>
   <p class="current-user mt-8">
     Signed in as <strong class="text-white font-normal"><%= current_user.cn %>@kosmos.org</strong>.
-    <%= link_to "Log out", destroy_user_session_path, method: :delete, class: 'underline' %>
+    <%= link_to "Log out", destroy_user_session_path, class: 'underline' %>
   </p>
 <% end %>

config/initializers/devise.rb

@@ -291,7 +291,7 @@ Devise.setup do |config|
   # config.navigational_formats = ['*/*', :html]
 
   # The default HTTP method used to sign out a resource. Default is :delete.
-  config.sign_out_via = :delete
+  config.sign_out_via = :get
 
   # ==> OmniAuth
   # Add a new OmniAuth provider. Check the wiki for more information on setting