Mark cssutils tests as xfail on Python >= 3.5

tests/unit/browser/test_mhtml.py

@@ -2,6 +2,7 @@
 import io
 import textwrap
 import re
+import sys
 
 import pytest
 
@@ -228,7 +229,12 @@ def test_empty_content_type(checker):
         """)
 
 
-@pytest.mark.parametrize('has_cssutils', [True, False])
+@pytest.mark.parametrize('has_cssutils', [
+    # TODO: remove xfail once new cssutils is released
+    pytest.mark.xfail(sys.version_info >= (3,5), reason='https://'
+                      'bitbucket.org/cthedot/cssutils/issues/52')(True),
+    False,
+])
 @pytest.mark.parametrize('inline, style, expected_urls', [
     (False, "@import 'default.css'", ['default.css']),
     (False, '@import "default.css"', ['default.css']),