Update lxml to 4.4.1

requirements.txt

@@ -14,7 +14,7 @@ cssselect==1.1.0
 -e git+https://github.com/mutalyzer/crossmapper.git#egg=crossmapper
 description-extractor==2.3.5
 interval-binning==1.0.0
-lxml==4.2.5
+lxml==4.4.1
 mock==1.3.0
 mockredispy==2.9.0.12
 pyparsing==2.0.5