Bump sphinx-rtd-theme from 2.0.0rc3 to 2.0.0rc4 #459

Job	Run time
publish-on-pypi	2m 30s
build-on-macos / build	10m 47s
build-on-ubuntu / build	4m 52s
build-installer-on-windows / build	8m 14s
build-on-windows / build	9m 17s
publish-on-github	51s
	36m 31s

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