Fix RTD build

[tsalo]

Take fixes from neurostuff/NiMARE#797 and readthedocs/readthedocs.org#10290.

[tsalo]

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/registry.py", line 442, in load_extension
    mod = import_module(extname)
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/builders/linkcheck.py", line 20, in <module>
    from requests import Response
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/requests/__init__.py", line 43, in <module>
    import urllib3
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/urllib3/__init__.py", line 38, in <module>
    raise ImportError(
ImportError: urllib3 v2.0 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with OpenSSL 1.0.2n  7 Dec 2017. See: https://github.com/urllib3/urllib3/issues/2168

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/cmd/build.py", line 280, in build_main
    app = Sphinx(args.sourcedir, args.confdir, args.outputdir,
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/application.py", line 225, in __init__
    self.setup_extension(extension)
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/application.py", line 404, in setup_extension
    self.registry.load_extension(self, extname)
  File "/home/docs/checkouts/readthedocs.org/user_builds/xcp-d/envs/877/lib/python3.8/site-packages/sphinx/registry.py", line 445, in load_extension
    raise ExtensionError(__('Could not import extension %s') % extname,
sphinx.errors.ExtensionError: Could not import extension sphinx.builders.linkcheck (exception: urllib3 v2.0 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with OpenSSL 1.0.2n  7 Dec 2017. See: https://github.com/urllib3/urllib3/issues/2168)

Extension error:
Could not import extension sphinx.builders.linkcheck (exception: urllib3 v2.0 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with OpenSSL 1.0.2n  7 Dec 2017. See: https://github.com/urllib3/urllib3/issues/2168)