[tools] Fix an error gflag description of 'kudu table scan'
[tools] Fix an error gflag description of 'kudu table scan'

Equal operator in gflag 'predicates' should be '=' but not '=='

Change-Id: I84f8f6958697f79d05c5b7f7ba3c438b05db639c
Reviewed-on: http://gerrit.cloudera.org:8080/12699
Tested-by: Kudu Jenkins
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@apache.org>

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