Bump lxml from 3.3.5 to 4.6.3 in /Holmes/fuzzers

Bumps [lxml](https://github.com/lxml/lxml) from 3.3.5 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-3.3.5...lxml-4.6.3)

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

Author: dependabot[bot]

Holmes/fuzzers/requirements.txt

@@ -1,5 +1,5 @@
 Twisted==14.0.0
-lxml==3.3.5
+lxml==4.6.3
 psutil==2.1.1
 pyasn1==0.1.7
 tlslite==0.4.6