RVM错误在High Sierra上安装ruby 2.3.0

Question

在将所有Pod命令（例如Pod安装，Pod更新）停止工作之后，我将macOS更新为High Sierra。谷歌搜索后，我建议将您的红宝石从2.0更新到2.3.0。但是使用rvm命令面临以下错误。

 Zubair-mac-mini:~ sdsol$ rvm install 2.3.0

 Searching for binary rubies, this might take some time.
 No binary rubies available for: osx/10.13/x86_64/ruby-2.3.0.
 Continuing with compilation. Please read 'rvm help mount' to get more 
 information on binary rubies.
 Checking requirements for osx.
 Installing requirements for osx.
 Updating system.........Failed to update Homebrew, follow instructions 
 here:
 https://github.com/Homebrew/homebrew/wiki/Common-Issues
 and make sure `brew update` works before continuing.
 ..
 Error running 'requirements_osx_brew_update_system ruby-2.3.0',
 please read /Users/sdsol/.rvm/log/1506680323_ruby-2.3.0/update_system.log
 Requirements installation failed with status: 1.
 Zubair-mac-mini:~ sdsol$ 

比我尝试更新自制软件，但是再没有运气会遇到另一个问题

 Zubair-mac-mini:~ sdsol$ brew update
 Error: /usr/local must be writable!

任何帮助将不胜感激。谢谢