Fix misconfigured test

This test needs the second argument to be a hash, the third argument is
intended for error message. This change is required for
rails-dom-testing 2.1.0 which now raises an error if you have a
misconfigured test (it was previously silent) [1].

[1]: rails/rails-dom-testing#96

test/functional/sitemap_controller_test.rb

@@ -21,7 +21,7 @@ class SitemapControllerTest < ActionController::TestCase
 
       assert_response :success
 
-      assert_select "url > loc", "http://www.dev.gov.uk/test-path", count: 1
+      assert_select "url > loc", { count: 1, text: "http://www.dev.gov.uk/test-path" }
     end
   end