[docs] sphinx_autodoc_typehints fails on RTD

[amotl]

Hi there,

apparently the sphinx_autodoc_typehints extension fails on RTD, see also https://readthedocs.org/projects/wetterdienst/builds/11889523/:

Running Sphinx v1.8.5
loading translations [en]... done

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/wetterdienst/envs/latest/lib/python3.7/site-packages/sphinx/registry.py", line 472, in load_extension
    mod = __import__(extname, None, None, ['setup'])
  File "/home/docs/checkouts/readthedocs.org/user_builds/wetterdienst/envs/latest/lib/python3.7/site-packages/sphinx_autodoc_typehints.py", line 8, in <module>
    from sphinx.util.inspect import signature as Signature
ImportError: cannot import name 'signature' from 'sphinx.util.inspect' (/home/docs/checkouts/readthedocs.org/user_builds/wetterdienst/envs/latest/lib/python3.7/site-packages/sphinx/util/inspect.py)

It might require a more recent installation of Sphinx?

With kind regards,
Andreas.

[amotl]

Same here: readthedocs/readthedocs.org#3734. Upgrading to Sphinx 3.2.1 fixed it, see 191f55a.