Update mkdocs-material to 5.5.6

[pyup-bot]

This PR updates mkdocs-material from 5.5.3 to 5.5.6.

Changelog

5.5.6

* Switched base template for 404.html to main.html
* Fixed 1864: GitHub organisation stats not loading

mkdocs-material-5.5.5+insiders-1.2.0 (2020-08-11)

* Added feature to expand navigation by default

5.5.5

* Fixed missing vendor and worker distribution files

5.5.4

* Added support for sortable data tables

Links

• PyPI: https://pypi.org/project/mkdocs-material
• Changelog: https://pyup.io/changelogs/mkdocs-material/
• Repo: https://squidfunk.github.io/mkdocs-material/

[coveralls]

Pull Request Test Coverage Report for Build 850

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.248%

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Totals
Change from base Build 841:	0.0%
Covered Lines:	1584
Relevant Lines:	1596

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💛 - Coveralls

[pyup-bot]

Closing this in favor of #144