Bump lxml from 3.6.4 to 4.9.1

Bumps [lxml](https://github.com/lxml/lxml) from 3.6.4 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-3.6.4...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

@@ -51,7 +51,7 @@ gsconfig==1.0.6
 gsimporter==1.0.0
 httplib2==0.9.2
 kombu==3.0.35
-lxml==3.6.4
+lxml==4.9.1
 mccabe==0.5.2
 oauthlib==2.0.1
 pep8==1.6.2