drk: fixed writing last scanned block to db

bin/drk/src/rpc_blockchain.rs

@@ -344,7 +344,7 @@ impl Drk {
             // Write down the slot number into back to the wallet
             // TODO: Why doesn't it work?
             let query = format!(
-                "INSERT INTO {} ({}) VALUES (?1);",
+                "UPDATE {} SET {} = ?1;",
                 MONEY_INFO_TABLE, MONEY_INFO_COL_LAST_SCANNED_SLOT
             );
             let params = json!([query, QueryType::Integer as u8, sl]);