Bump lxml from 3.6.0 to 4.6.3

Bumps [lxml](https://github.com/lxml/lxml) from 3.6.0 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-3.6.0...lxml-4.6.3)

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

dev-requirements.txt

@@ -5,18 +5,40 @@
 #    pip-compile dev-requirements.in
 #
 check-manifest==0.31
-click==6.4                # via pip-tools
+    # via -r dev-requirements.in
+click==6.4
+    # via pip-tools
 coverage==4.0.3
+    # via -r dev-requirements.in
 detox==0.10.0
-eventlet==0.18.4          # via detox
-first==2.0.1              # via pip-tools
-greenlet==0.4.9           # via eventlet
-lxml==3.6.0
+    # via -r dev-requirements.in
+eventlet==0.18.4
+    # via detox
+first==2.0.1
+    # via pip-tools
+greenlet==0.4.9
+    # via eventlet
+lxml==4.6.3
+    # via -r dev-requirements.in
 nose==1.3.7
+    # via -r dev-requirements.in
 pip-tools==1.6
-pluggy==0.3.1             # via tox
-py==1.4.31                # via detox, tox
-six==1.10.0               # via pip-tools, xunitmerge
+    # via -r dev-requirements.in
+pluggy==0.3.1
+    # via tox
+py==1.4.31
+    # via
+    #   detox
+    #   tox
+six==1.10.0
+    # via
+    #   pip-tools
+    #   xunitmerge
 tox==2.3.1
-virtualenv==15.0.1        # via tox
+    # via
+    #   -r dev-requirements.in
+    #   detox
+virtualenv==15.0.1
+    # via tox
 xunitmerge==1.0.4
+    # via -r dev-requirements.in