DOC: doc build failing as apparent change in statsmodel url
```
intersphinx inventory 'https://www.statsmodels.org/devel/objects.inv' not fetchable due to <class 'requests.exceptions.ConnectionError'>: HTTPSConnectionPool(host='www.statsmodels.org', port=443): Max retries exceeded with url: /devel/objects.inv (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7fcc923600a0>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution'))
```