错误代码：curl: (56) LibreSSL SSL_read: SSL_ERROR_SYSCALL, errno 54

==> Downloading https://yarnpkg.com/downloads/1.6.0/yarn-v1.6.0.tar.gz
==> Downloading from https://github.com/yarnpkg/yarn/releases/download/v1.6.0/yarn-v1.6.0.tar.gz
###########################                                               38.6%
curl: (56) LibreSSL SSL_read: SSL_ERROR_SYSCALL, errno 54
######################################################################## 100.0%
curl: (7) Failed to connect to github-production-release-asset-2e65be.s3.amazonaws.com port 443: Operation timed out
Error: Failed to download resource "yarn"
Download failed: https://yarnpkg.com/downloads/1.6.0/yarn-v1.6.0.tar.gz

原因应该是 curl 有问题，将 homebrew 源切换成中科院的源也无法解决问题！

最后找到一种方式解决了，在 Mac 终端输入如下命令：

$ git config --global core.compression -1

然后重新安装 yarn（由于电脑安装了 node，所以带上 --without-node 参数）

$ brew install yarn --without-node
==> Downloading https://yarnpkg.com/downloads/1.6.0/yarn-v1.6.0.tar.gz
==> Downloading from https://github.com/yarnpkg/yarn/releases/download/v1.6.0/yarn-v1.6.0.tar.gz
######################################################################## 100.0%
🍺  /usr/local/Cellar/yarn/1.6.0: 14 files, 4.1MB, built in 4 minutes 58 seconds