Fix false possitive test

This test was passing because the assert_dom_equal was only comparing
the top level tag.

This bug was fixed at
rails/rails-dom-testing@c06500c
and released as rails-dom-testing 1.0.3

Author: Rafael Mendonça França

test/sanitizer_test.rb

@@ -173,7 +173,7 @@ def test_sanitize_image_src
   end
 
   def test_should_allow_anchors
-    assert_sanitized %(<a href="foo" onclick="bar"><script>baz</script></a>), %(<a href=\"foo\">baz</a>)
+    assert_sanitized %(<a href="foo" onclick="bar"><script>baz</script></a>), %(<a href=\"foo\"></a>)
   end
 
   def test_video_poster_sanitization