Update mistune to 0.7.4

[pyup-bot]

There's a new version of mistune available.
You are currently using 0.7.1. I have updated it to 0.7.4

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

Changelog

0.7.4

Released on Mar. 14, 2017

• Fix escape_link method by Marcos Ojeda
• Handle block HTML with no content by David Baumgold
• Use expandtabs for tab
• Fix escape option for text renderer
• Fix HTML attribute regex pattern

0.7.3

Released on Jun. 28, 2016

• Fix strikethrough regex
• Fix HTML attribute regex
• Fix close tag regex

0.7.2

Released on Feb. 26, 2016

• Fix hard_wrap options on renderer.
• Fix emphasis regex pattern
• Fix base64 image link 80_.
• Fix link security per 87_.

.. _80: lepture/mistune#80
.. _87: lepture/mistune#87

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

Happy merging! 🤖