build(deps): bump lxml from 4.3.3 to 4.6.2

Bumps [lxml](https://github.com/lxml/lxml) from 4.3.3 to 4.6.2.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.3.3...lxml-4.6.2)

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

requirements.txt

@@ -172,7 +172,7 @@ jupyter-client==5.2.4
 jupyter-core==4.4.0
 kombu==4.4.0
 limits==1.3
-lxml==4.3.3
+lxml==4.6.2
 Mako==1.0.8
 MarkupSafe==1.1.1
 marshmallow==2.20.5