Merge pull request #116 from adamchainz/readthedocs.io

Convert readthedocs links for their .org -> .io migration for hosted projects

docs/source/conf.py

@@ -367,5 +367,5 @@
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     'python': ('https://docs.python.org/', None),
-    'redis': ('https://redis-py.readthedocs.org/en/latest/', None)
+    'redis': ('https://redis-py.readthedocs.io/en/latest/', None)
 }