private <T> T execute(JedisTask<T> task) {
    T result;
    try (Jedis jedis = pool.getResource()) {
      result = task.run(jedis);
    }
    return result;
  }
Default implementation for {@link JedisTaskExecutor} which is the Jedis wrapper used to access
Redis.

TODO(zheng): support redis cluster.
src/main/java/com/eudemon/ratelimiter/redis/DefaultJedisTaskExecutor.java