Update intersphinx linking to python.org

We're getting a message in the docs build about the intersphinx location
having moved. This moves it accordingly.

Running Sphinx v1.5.2
loading pickled environment... not yet created
loading intersphinx inventory from
http://docs.python.org/3/objects.inv...
intersphinx inventory has moved: http://docs.python.org/3/objects.inv ->
https://docs.python.org/3/objects.inv

Change-Id: I9ae3fd19a157dfcee0357ddfaab9e8933af7624c

doc/source/conf.py

@@ -120,7 +120,7 @@ latex_documents = [
 ]
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'http://docs.python.org/3/': None}
+intersphinx_mapping = {'https://docs.python.org/3/': None}
 
 # Include both the class and __init__ docstrings when describing the class
 autoclass_content = "both"