Proxy configure doesn't work #15
Description
When we set env http_proxy and env https_proxy, the request doesn't go with proxy configure. It seems the SDK doesn't supply proxy because of the way which the SDK use of the fasthttp lib.
We need to set a proxy dial when creating the fasthttp client for using proxy. But
the aliyun-mns-go-sdk uses the default dial. What's more, the env "MNS_GLOBAL_PROXY" defined in aliyun-mns-go-sdk looks like using for proxy, but it doesn't work.