Set Alchemy.logout_method to Devise.sign_out_via

Keep these two in sync.

Author: tvdeyen

config/initializers/alchemy.rb

@@ -18,3 +18,9 @@
 Alchemy.signup_path     = '/admin/signup'
 Alchemy.login_path      = '/admin/login'
 Alchemy.logout_path     = '/admin/logout'
+
+if Alchemy.respond_to?(:logout_method)
+  Rails.application.config.after_initialize do
+    Alchemy.logout_method = Devise.sign_out_via
+  end
+end