Fix checkstyle documentation

This is following the style of the artifact-resolver builder, which
has other nested dictionaries also.

Change-Id: I26b909e18239df03c123e07791fa7a3549be7701
Reviewed-on: https://review.openstack.org/23977
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: Antoine Musso <hashar@free.fr>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins