Update requirements in docs

[jnovinger]

This updates a couple of docs/ files to reflect changes made in #839 .

[jnovinger]

Apologies, I missed noting these in the previous PR, so thought I would throw them up real quick.

[jnovinger]

Also, I'm not familiar enough with Sphinx anymore to know what needs to be done re:

djangorestframework-simplejwt/docs/conf.py

Lines 306 to 311 in 7f300a2

	# -- Intersphinx configuration ------------------------------------------------
	intersphinx_mapping = {
	"python": ("https://docs.python.org/3.8", None),
	}

Ah, it looks to just be configuration for Sphinx's Intersphinx plugin. I didn't see any usage of the python target anywhere following some quick grepping.

[Andrew-Chen-Wang]

Thank you!