docs: Fix conf.py for Sphinx 2.0

Our version check in Documentation/conf.py never envisioned a world where
Sphinx moved beyond 1.x.  Now that the unthinkable has happened, fix our
version check to handle higher version numbers correctly.

Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed