Update db_bench_tool.cc (#1239)
Update db_bench_tool.cc (#1239)

* Update db_bench_tool.cc

* Update db_bench_tool.cc

SunguckLee/RocksDB,wat-ze-hex/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,wenduo/rocksdb,facebook/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,facebook/rocksdb,wenduo/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,vmx/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,wenduo/rocksdb,facebook/rocksdb,SunguckLee/RocksDB,OverlordQ/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,norton/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,OverlordQ/rocksdb,norton/rocksdb,facebook/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,norton/rocksdb,bbiao/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,vmx/rocksdb,wat-ze-hex/rocksdb,SunguckLee/RocksDB,norton/rocksdb,tsheasha/rocksdb,norton/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,norton/rocksdb,wenduo/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,wat-ze-hex/rocksdb,tsheasha/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,vmx/rocksdb,bbiao/rocksdb,wat-ze-hex/rocksdb,OverlordQ/rocksdb,Andymic/rocksdb,tsheasha/rocksdb,facebook/rocksdb,Andymic/rocksdb,Andymic/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,norton/rocksdb,hobinyoon/rocksdb,facebook/rocksdb,facebook/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,vmx/rocksdb,tsheasha/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,vmx/rocksdb