update for proxies

[soondh]

我们的oss是部署在专有云环境中的，sdk需要走一层代理，目前代理只能通过设置全局代理，有点不方便。
在bucket初始化的时候添加代理选项，后续会方便一点。

bucket = oss2.Bucket(auth, endpoint, bucketName, proxies=proxies_pool)

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