国内镜像

修改~/.cargo/config 文件，如果没有就创建

[source.crates-io]
registry = "https://github.com/rust-lang/crates.io-index"

replace-with = 'tuna'
[source.tuna]
registry = "https://mirrors.tuna.tsinghua.edu.cn/git/crates.io-index.git"

#replace-with = 'ustc'
#[source.ustc]
#registry = "git://mirrors.ustc.edu.cn/crates.io-index"