Merge pull request #98 from mozilla-services/pyup-update-pytest-html-1.17.0-to-1.18.0

Update pytest-html to 1.18.0

Author: stephendonner

axe_selenium_python/tests/requirements/tests.txt

@@ -1,5 +1,5 @@
 pytest==3.6.0
 selenium==3.12.0
 pytest-selenium==1.13.0
-pytest-html==1.17.0
+pytest-html==1.18.0
 pytest_base_url==1.4.1