Switch to using hashbrown version of HashMap and (#2158)

HashSet for improved performance and memory usage

src/thin_client.rs

@@ -11,6 +11,7 @@ use crate::result::{Error, Result};
 use crate::rpc_request::{RpcClient, RpcRequest};
 use bincode::serialize;
 use bs58;
+use hashbrown::HashMap;
 use log::Level;
 use serde_json;
 use solana_metrics;
@@ -23,7 +24,6 @@ use solana_sdk::system_transaction::SystemTransaction;
 use solana_sdk::timing;
 use solana_sdk::transaction::Transaction;
 use std;
-use std::collections::HashMap;
 use std::io;
 use std::net::{SocketAddr, UdpSocket};
 use std::sync::atomic::AtomicBool;