Update lxml to 3.6.4

[pyup-bot]

There's a new version of lxml available.
You are currently using 3.6.0. I have updated it to 3.6.4

These links might come in handy: PyPI | Changelog | Homepage

Changelog

3.6.4

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

• GH204, LP1614693: build fix for MacOS-X.

3.6.3

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

• LP1614603: change linker flags to build multi-linux wheels

3.6.2

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

• LP1614603: release without source changes to provide cleanly built Linux wheels

3.6.1

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

Features added

• GH180: Separate option inline_style for Cleaner that only removes style
  attributes instead of all styles. Patch by Christian Pedersen.

• GH196: Windows build support for Python 3.5. Contribution by Maximilian Hils.

Bugs fixed

• GH199: Exclude file fields from FormElement.form_values (as browsers do).
  Patch by Tomas Divis.

• GH198, LP1568167: Try to provide base URL from Resolver.resolve_string().
  Patch by Michael van Tellingen.

• GH191: More accurate float serialisation in objectify.FloatElement.
  Patch by Holger Joukl.

• LP1551797: Repair XSLT error logging. Patch by Marcus Brinkmann.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[codecov-io]

Current coverage is 100% (diff: 100%)

Merging #139 into master will not change coverage

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  Misses          0      0          
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[pyup-bot]

Closing this in favor of #144