Update markdown to 3.6

[pyup-bot]

This PR updates markdown from 3.4.1 to 3.6.

Changelog

3.5.2

Fixed

* Fix type annotations for `convertFile` - it accepts only bytes-based buffers.
Also remove legacy checks from Python 2 (1400)
* Remove legacy import needed only in Python 2 (1403)
* Fix typo that left the attribute `AdmonitionProcessor.content_indent` unset
(1404)
* Fix edge-case crash in `InlineProcessor` with `AtomicString` (1406).
* Fix edge-case crash in `codehilite` with an empty `code` tag (1405).
* Improve and expand type annotations in the code base (1401).
* Fix handling of bogus comments (1425).

3.5.1

Fixed

* Fix a performance problem with HTML extraction where large HTML input could
trigger quadratic line counting behavior (1392).
* Improve and expand type annotations in the code base (1394).

Links

• PyPI: https://pypi.org/project/markdown
• Changelog: https://data.safetycli.com/changelogs/markdown/

[pyup-bot]

Closing this in favor of #216