chore(deps): update dependency sphinx-rtd-theme to v3

This MR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
sphinx-rtd-theme	~1.0 -> ~3.0

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Release Notes

readthedocs/sphinx_rtd_theme (sphinx-rtd-theme)

v3.0.2

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v3.0.1

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v3.0.0

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v2.0.0

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v1.3.0

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v1.2.2

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v1.2.1

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v1.2.0

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v1.1.1

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v1.1.0

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Configuration

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