Update sphinx-bootstrap-theme to 0.6.0

[pyup-bot]

There's a new version of sphinx-bootstrap-theme available.
You are currently using 0.4.14. I have updated it to 0.6.0

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

Changelog

0.5.3

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• Fix sidebar jQuery issue with height. (Sheile)
  157 <https://github.com/ryan-roemer/sphinx-bootstrap-theme/pull/157>.

0.5.2

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bad release

0.5.1

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• Fix import url() CSS imports to be relative paths so that you can have a
  non-root / nested site.

0.5.0

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• Fix css_files breakage from Sphinx 1.6+ update.
  158 <https://github.com/ryan-roemer/sphinx-bootstrap-theme/pull/158>,
  160 <https://github.com/ryan-roemer/sphinx-bootstrap-theme/pull/160>.

• Breaking Change: Remove bootswatch_css_custom override, and instead opt for documenting idiomatic Sphinx-version specific generic overrides for custom CSS.

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

Happy merging! 🤖