Update nbsphinx to 0.7.0

[pyup-bot]

This PR updates nbsphinx from 0.5.0 to 0.7.0.

Changelog

0.7.0

* Warnings can be suppressed with ``suppress_warnings``.
* ``<img>`` tags are handled in Markdown cells; the ``alt``, ``width``,
``height`` and ``class`` attributes are supported.
* CSS: prompts protrude into left margin if ``nbsphinx_prompt_width`` is
too small. If you want to hide the prompts, use `custom CSS`__.

__ https://nbsphinx.readthedocs.io/en/0.7.0/custom-css.html

0.6.1

* ``.ipynb_checkpoints`` is automatically added to ``exclude_patterns``

0.6.0

* Thumbnail galleries (inspired by https://sphinx-gallery.github.io/)
* ``nbsphinx-toctree`` as cell tag
* Keyword arguments in ``nbsphinx_custom_formats``
* Python 2 support has been dropped

0.5.1

* This will be the last release supporting Python 2.x!
* Support for https://github.com/choldgraf/sphinx-copybutton
* Executed notebooks are now saved in the HTML output directory

Links

• PyPI: https://pypi.org/project/nbsphinx
• Changelog: https://pyup.io/changelogs/nbsphinx/
• Docs: https://nbsphinx.readthedocs.io/