Bump lxml from 4.6.5 to 4.9.1

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.5 to 4.9.1.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](https://github.com/lxml/lxml/compare/lxml-4.6.5...lxml-4.9.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -2,7 +2,7 @@ pandas==0.20.3
 setuptools==40.4.3
 pytz==2017.2
 Requests==2.20.0
-lxml==4.6.5
+lxml==4.9.1
 future-fstrings
 bs4
 jira