No light theme available in docs

[jorgepiloto]

🐞 Problem
There is no button or slider to allow switching to "light" mode in documentation for versions:

• Version 1.4.0: https://numpydoc.readthedocs.io/en/v1.4.0/
• Stable: https://numpydoc.readthedocs.io/en/stable/
• Latest: https://numpydoc.readthedocs.io/en/latest/

However, version 1.3.1 seems to have the light mode enabled:

• Version 1.3.1: https://numpydoc.readthedocs.io/en/v1.3.1/

[rossbar]

Thanks for the report @jorgepiloto , you are indeed correct. This should be fixed by #414, though it will require a new doc deploy to get the update into the published site.