Update models.rst
Update models.rst

Fix typo in model docs
kbarbary/sncosmo,dannygoldstein/sncosmo,dannygoldstein/sncosmo,sncosmo/sncosmo,kbarbary/sncosmo,sncosmo/sncosmo,kbarbary/sncosmo,sncosmo/sncosmo,dannygoldstein/sncosmo