Fix readthedocs build failure on `urllib3==2.0.0`

[mesozoic]

Related to #251, we're now seeing readthedocs builds fail (like this one). I'm poking at things in the new configuration file format to see how I can get this working again.

Sample traceback:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/sphinx/config.py", line 327, in eval_config_file
    exec(code, namespace)
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/checkouts/latest/docs/source/conf.py", line 7, in <module>
    from pyairtable import __version__ as version
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/pyairtable-1.4.0-py3.7.egg/pyairtable/__init__.py", line 3, in <module>
    from .api import Api, Base, Table  # noqa
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/pyairtable-1.4.0-py3.7.egg/pyairtable/api/__init__.py", line 1, in <module>
    from .api import Api  # noqa
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/pyairtable-1.4.0-py3.7.egg/pyairtable/api/api.py", line 3, in <module>
    from .abstract import ApiAbstract, TimeoutTuple
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/pyairtable-1.4.0-py3.7.egg/pyairtable/api/abstract.py", line 8, in <module>
    import requests
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/requests/__init__.py", line 43, in <module>
    import urllib3
  File "/home/docs/checkouts/readthedocs.org/user_builds/pyairtable/envs/latest/lib/python3.7/site-packages/urllib3/__init__.py", line 39, in <module>
    "urllib3 v2.0 only supports OpenSSL 1.1.1+, currently "
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

[codecov-commenter]

Codecov Report

Merging #253 (182b4c9) into main (1f9797f) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 182b4c9 differs from pull request most recent head b06baa6. Consider uploading reports for the commit b06baa6 to get more accurate results

@@           Coverage Diff           @@
##             main     #253   +/-   ##
=======================================
  Coverage   87.61%   87.61%           
=======================================
  Files          14       14           
  Lines         662      662           
=======================================
  Hits          580      580           
  Misses         82       82