优化 RedisConnection，采用单例模式导出

src/lib/Database/RedisConnection.ts

@@ -39,5 +39,6 @@ class RedisConnection {
     }
 }
 
-const redisConnection = new RedisConnection();
-export default redisConnection.getPool();
+const _redisConnection = new RedisConnection();
+const redisConnection = _redisConnection.getPool();
+export default redisConnection;