Update lxml to 4.2.4

[pyup-bot]

This PR updates lxml from 4.1.1 to 4.2.4.

Changelog

4.2.3

==================

Bugs fixed
----------

* Reverted GH265: lxml links against zlib as a shared library again.

4.2.2

==================

Bugs fixed
----------

* GH266: Fix sporadic crash during GC when parse-time schema validation is used
and the parser participates in a reference cycle.
Original patch by Julien Greard.

* GH265: lxml no longer links against zlib as a shared library, only on static builds.
Patch by Nehal J Wani.

4.2.1

==================

Bugs fixed
----------

* LP1755825: ``iterwalk()`` failed to return the 'start' event for the initial
element if a tag selector is used.

* LP1756314: Failure to import 4.2.0 into PyPy due to a missing library symbol.

* LP1727864, GH258: Add "-isysroot" linker option on MacOS as needed by XCode 9.

4.2.0

==================

Features added
--------------

* GH255: ``SelectElement.value`` returns more standard-compliant and
browser-like defaults for non-multi-selects.  If no option is selected, the
value of the first option is returned (instead of None).  If multiple options
are selected, the value of the last one is returned (instead of that of the
first one).  If no options are present (not standard-compliant)
``SelectElement.value`` still returns ``None``.

* GH261: The ``HTMLParser()`` now supports the ``huge_tree`` option.
Patch by stranac.

Bugs fixed
----------

* LP1551797: Some XSLT messages were not captured by the transform error log.

* LP1737825: Crash at shutdown after an interrupted iterparse run with XMLSchema
validation.

Other changes
-------------

Links

• PyPI: https://pypi.org/project/lxml
• Changelog: https://pyup.io/changelogs/lxml/
• Homepage: http://lxml.de/
• Bugtracker: https://bugs.launchpad.net/lxml

[coveralls]

Coverage decreased (-0.04%) to 30.441% when pulling a781a14 on pyup-update-lxml-4.1.1-to-4.2.4 into 5bb5c99 on master.

[pyup-bot]

Closing this in favor of #197