logging: [doc] Fix a typo

/var/log/glusterd/logger.conf should be /var/lib/glusterd/logger.conf

Change-Id: I3a4b19eb59d7acf83224fed01a5856565ffe1741
BUG: 928648
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/5466
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Anand Avati <avati@redhat.com>