[docs] fix typo in location-awareness design doc
[docs] fix typo in location-awareness design doc

Fixed scan mode name: READ_CLOSEST --> CLOSEST_REPLICA

Change-Id: I28f7ea1137561fbb94096d6b41b69adeec19693f
Reviewed-on: http://gerrit.cloudera.org:8080/14196
Tested-by: Kudu Jenkins
Reviewed-by: Andrew Wong <b68e4fdc6430321a6b47400732ff97d7ae91234e@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu