Unpin the Sphinx version

[seisman]

Description of proposed changes

Fixes #

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

[weiji14]

So sphinx and sphinx_rtd_theme was pinned at #383, and the main change I notice is a condensed API documentation?

Old (current):

New (This PR):

Doesn't look too bad 😄

[seisman]

It wastes too many spaces on the left side.

[weiji14]

Yeah it does. I do like how the vertical whitespace is compressed (for the Aliases especially). Maybe we can configure it somehow (looking at https://sphinx-rtd-theme.readthedocs.io/en/stable/index.html), or pin to a different version?

[seisman]

Note that we also have a custom style.css which may or may not be compatible with new sphinx and sphinx_rtd_theme.

[seisman]

It seems unpinning the sphinx version doesn't change the appearance of the API documentation.

Can we merge the PR?

[weiji14]

Interesting, good to unpin it then!