Fix django_db_modify_db_settings_xdist_suffix doc (#437)

Author: alexeykuz

docs/database.rst

@@ -201,7 +201,7 @@ Requesting this fixture will add a suffix to the database name when the tests
 are run via pytest-xdist.
 
 This fixture is by default requsted from
-:fixture:`django_db_modify_db_settings_xdist_suffix`.
+:fixture:`django_db_modify_db_settings`.
 
 django_db_use_migrations
 """"""""""""""""""""""""