Update markdown to 2.6.8

[pyup-bot]

There's a new version of markdown available.
You are currently using 2.2.1. I have updated it to 2.6.8

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

Changelog

2.6

next_url: release-2.6.html

Python-Markdown Change Log

Sept 23, 2016: Released version 2.6.7 (a bug-fix release).

Mar 20, 2016: Released version 2.6.6 (a bug-fix release).

Nov 24, 2015: Released version 2.6.5 (a bug-fix release).

Nov 6, 2015: Released version 2.6.4 (a bug-fix release).

Oct 26, 2015: Released version 2.6.3 (a bug-fix release).

Apr 20, 2015: Released version 2.6.2 (a bug-fix release).

Mar 8, 2015: Released version 2.6.1 (a bug-fix release). The (new)
yaml option has been removed from the Meta-Data Extension as it was buggy
(see 390).

Feb 19, 2015: Released version 2.6 (Notes).

Nov 19, 2014: Released version 2.5.2 (a bug-fix release).

Sept 26, 2014: Released version 2.5.1 (a bug-fix release).

Sept 12, 2014: Released version 2.5.0 (Notes).

Feb 16, 2014: Released version 2.4.0 (Notes).

Mar 22, 2013: Released version 2.3.1 (a bug-fix release).

Mar 14, 2013: Released version 2.3.0 (Notes)

Nov 4, 2012: Released version 2.2.1 (Notes).

Jul 5, 2012: Released version 2.2.0 (Notes).

Jan 22, 2012: Released version 2.1.1 (Notes).

Nov 24, 2011: Released version 2.1.0 (Notes).

Oct 7, 2009: Released version 2.0.3.

Sept 28, 2009: Released version 2.0.2 (Notes).

May 20, 2009: Released version 2.0.1 (Notes).

Mar 30, 2009: Released version 2.0 (Notes).

Mar 8, 2009: Release Candidate 2.0-rc-1.

Feb 2009: Added support for multi-level lists to new Blockprocessors.

Jan 2009: Added HTML 4 output as an option (thanks Eric Abrahamsen)

Nov 2008: Added Definition List ext. Replaced old core with Blockprocessors.
Broken up into multiple files.

Oct 2008: Changed logging behavior to work better with other systems.
Refactored tree traversing. Added treap implementation, then replaced with
OrderedDict. Renamed various processors to better reflect what they actually
do. Refactored footnote ext to match PHP Extra's output.

Sept 2008: Moved prettifyTree to a Postprocessor, replaced WikiLink ext
with WikiLinks (note the s) ext (uses bracketed links instead of CamelCase)
and various bug fixes.

August 18 2008: Reorganized directory structure. Added a 'docs' directory
and moved all extensions into a 'markdown-extensions' package.

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

Happy merging! 🤖