Update lxml to 4.3.4

[pyup-bot]

This PR updates lxml from 4.2.5 to 4.3.4.

Changelog

4.3.4

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

* Rebuilt with Cython 0.29.10 to support Python 3.8.

4.3.3

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

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

* Fix leak of output buffer and unclosed files in ``_XSLTResultTree.write_output()``.

4.3.2

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

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

* Crash in 4.3.1 when appending a child subtree with certain text nodes.

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

* Built with Cython 0.29.6.

4.3.1

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

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

* LP1814522: Crash when appending a child subtree that contains unsubstituted
entity references.

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

* Built with Cython 0.29.5.

4.3.0

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

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

* The module ``lxml.sax`` is compiled using Cython in order to speed it up.

* GH267: ``lxml.sax.ElementTreeProducer`` now preserves the namespace prefixes.
If two prefixes point to the same URI, the first prefix in alphabetical order
is used.  Patch by Lennart Regebro.

* Updated ISO-Schematron implementation to 2013 version (now MIT licensed)
and the corresponding schema to the 2016 version (with optional "properties").

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

* GH270, GH271: Support for Python 2.6 and 3.3 was removed.
Patch by hugovk.

* The minimum dependency versions were raised to libxml2 2.9.2 and libxslt 1.1.27,
which were released in 2014 and 2012 respectively.

* Built with Cython 0.29.2.

4.2.6

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

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

* LP1799755: Fix a DeprecationWarning in Py3.7+.

* Import warnings in Python 3.6+ were resolved.

Links

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

[coveralls]

Coverage decreased (-0.7%) to 94.04% when pulling 01c1b20 on pyup-update-lxml-4.2.5-to-4.3.4 into 528af0a on master.

[pyup-bot]

Closing this in favor of #93