Bump lxml from 4.4.2 to 4.6.3 in /dr

Bumps [lxml](https://github.com/lxml/lxml) from 4.4.2 to 4.6.3.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.4.2...lxml-4.6.3)

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

Author: dependabot[bot]

dr/requirements.txt

@@ -52,7 +52,7 @@ jupyter-highlight-selected-word==0.2.0
 jupyter-latex-envs==1.4.6
 jupyter-nbextensions-configurator==0.4.1
 lazy-object-proxy==1.4.3
-lxml==4.4.2
+lxml==4.6.3
 MarkupSafe==1.1.1
 mccabe==0.6.1
 mistune==0.8.4