Fix admin logout feature spec

Update the admin logout feature spec to accommodate the UI changes 
in the admin navigation bar.
The 'Logout' link is now nested within a 'details' tag and must
be clicked/expanded to access the logout functionality.

Author: rainerdema

spec/features/admin/sign_out_spec.rb

@@ -15,9 +15,28 @@
   end
 
   scenario 'allows a signed in user to logout' do
-    click_link 'Logout'
+    click_logout_link
     visit spree.admin_login_path
     expect(page).to have_text 'Login'
     expect(page).not_to have_text 'Logout'
   end
+
+  def click_logout_link
+    new_version? ? logout_new_version : logout_old_version
+  end
+
+  def new_version?
+    Gem::Requirement.new('>= 4.2').satisfied_by?(Spree.solidus_gem_version)
+  end
+
+  def logout_new_version
+    find('details div', text: user.email, wait: 10).click
+    within('details') do
+      click_link 'Logout'
+    end
+  end
+
+  def logout_old_version
+    click_link 'Logout'
+  end
 end