MAC升级mojave导致sass无法安装使用

升级完系统，发现一些问题,如sass无法使用了:
先解决这个问题：

xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun

解决方法，重装xcode command line：

 xcode-select --install

这里如果命令安装不了，可以手动下载 Command_Line_Tools_macOS_10.14_for_Xcode_10.1
如果没有解决问题，执行以下命令

sudo xcode-select -switch /

升级ruby

 brew install ruby

查看sass版本，报一下错误：

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接下来我升级了gem
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gem如果出现这种情况，由于sources源问题导致

huangjihua@huangjihuadeMacBook-Pro-2  ~  gem update --system
ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)
    bad response Not Found 404 (https://gems.ruby-china.org/specs.4.8.gz)

huangjihua@huangjihuadeMacBook-Pro-2  ~  gem sources
*** CURRENT SOURCES ***

https://gems.ruby-china.org
https://gems.ruby-china.com/

huangjihua@huangjihuadeMacBook-Pro-2  ~  gem sources --remove https://gems.ruby-china.org
https://gems.ruby-china.org removed from sources
huangjihua@huangjihuadeMacBook-Pro-2  ~  gem update --system
Latest version already installed. Done.

升级gem出现了错误

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升级完之后，重新安装sass

sudo gem install -n /usr/local/bin sass

大功告成！

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