Update Sphinx configuration.

docs/conf.py

@@ -358,6 +358,4 @@ epub_exclude_files = ['search.html']
 # If false, no index is generated.
 #epub_use_index = True
 
-
-# Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'https://docs.python.org/3/': None}
+intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}