Bump lxml from 4.5.2 to 4.6.2 in /css

Bumps [lxml](https://github.com/lxml/lxml) from 4.5.2 to 4.6.2.
- [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-4.5.2...lxml-4.6.2)

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/css/requirements.txt b/css/requirements.txt
index 725ddd9..28b2040 100644
--- a/css/requirements.txt
+++ b/css/requirements.txt
@@ -1,6 +1,6 @@
 Template-Python==0.1.post1
 html5lib==1.1
-lxml==4.5.2
+lxml==4.6.2
 mercurial==4.5
 six==1.15.0
 webencodings==0.5.1