Fix sphinx-autodoc-typehints requires on RTD
Fix sphinx-autodoc-typehints requires on RTD

This fixes build problem on RTD.  For some odd reason,
sphinx-autodoc-typehints fails to pull in requires Sphinx version on
RTD.  I have not been able to reproduce this myself, so the Sphinx
version requirement is used as a workaround for now.

Signed-off-by: Esben Haabendal <da90c138e4a9573086862393cde34fa33d74f6e5@haabendal.dk>

XD-embedded/xd-docker,XD-embedded/xd-docker,esben/xd-docker,esben/xd-docker