Bump lxml from 4.6.3 to 4.9.1

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.3 to 4.9.1.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.6.3...lxml-4.9.1)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -14,7 +14,7 @@ flake8==3.8.4
 djangorestframework==3.11.0
 djangorestframework-httpsignature==1.0.0
 djangocms-admin-style==1.2.7
-lxml==4.6.3
+lxml==4.9.1
 beautifulsoup4==4.6.0
 pyOpenSSL==17.5.0
 google-api-python-client==1.6.5