Bump lxml from 3.4.4 to 4.6.3

Bumps [lxml](https://github.com/lxml/lxml) from 3.4.4 to 4.6.3.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](https://github.com/lxml/lxml/commits/lxml-4.6.3)

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

requirements.txt

@@ -5,5 +5,5 @@
 # Custom version of scraperwiki library
 -e git+http://github.com/openaustralia/scraperwiki-python.git@morph_defaults#egg=scraperwiki
 
-lxml==3.4.4
+lxml==4.6.3
 cssselect==0.9.1