remove compilation warning.  all is calm, for now
remove compilation warning.  all is calm, for now

tempbottle/rust-rocksdb,spacejam/rust-rocksdb,tempbottle/rust-rocksdb,spacejam/rust-rocksdb,Lingling7/rust-rocksdb,tempbottle/rust-rocksdb,zhangjinpeng1987/rust-rocksdb,kaedroho/rust-rocksdb,dgrnbrg/rust-rocksdb,spacejam/rust-rocksdb,kaedroho/rust-rocksdb,kaedroho/rust-rocksdb,zhangjinpeng1987/rust-rocksdb