Update `shell` command so it works with ipython.

Updated to 0b8fa2adb106aaf368e812ae769d029d613cda42 (latest change in
master)
https://github.com/django-extensions/django-extensions/blob/master/django_extensions/management/commands/shell_plus.py

Change-Id: I462490ce84d9bea49db40d73bb7103038e2914b7
Merge "Update `shell` command so it works with ipython."