Bump lxml from 4.1.0 to 4.6.2

Bumps [lxml](https://github.com/lxml/lxml) from 4.1.0 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-4.1.0...lxml-4.6.2)

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

requirements.txt

@@ -2,7 +2,7 @@ backports-abc==0.5
 certifi==2017.7.27.1
 chardet==3.0.4
 idna==2.6
-lxml==4.1.0
+lxml==4.6.2
 requests==2.18.4
 singledispatch==3.4.0.3
 six==1.11.0