如果因为网络问题请求 pub.dev 失败：
Got socket error trying to find package ....
可以尝试切换数据源：
echo 'export PUB_HOSTED_URL=https://mirrors.tuna.tsinghua.edu.cn/dart-pub' >> ~/.zshrc
或者
echo 'export PUB_HOSTED_URL=https://mirrors.aliyun.com/dart-pub' >> ~/.zshrc
或者
export PUB_HOSTED_URL=https://mirrors.cloud.tencent.com/dart-pub
然后
source ~/.zshrc
cd iOS pod install
