Fix deprecated intersphinx_mapping format

This updates the format for `intersphinx_mapping` to use the actively maintained format. The previous format has been deprecated for a while and is slated to be removed in the next major release of Sphinx.

docs/conf.py

@@ -316,5 +316,5 @@ def find_version(*file_paths):
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {"https://docs.python.org/": None}
+intersphinx_mapping = {"python": ("https://docs.python.org/3/", None)}
 html_theme = "alabaster"