Documentation claims the version is still 2.17.0

The sphinx configuration still has the version as 2.17, so the `<title>` on https://babel.pocoo.org/en/latest/index.html is outdated. https://github.com/python-babel/babel/blob/56c63caf50b18b152541b5dcafd51f645d867074/docs/conf.py#L53-L56 Perhaps this should be changed to extract the version from `babel/__init__.py`.