现象：
yuwentekiMacBook-Pro:~ yuwen$ brew install node /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/universal-darwin16/rbconfig.rb:213: warning: Insecure world writable dir /usr/local/mysql/bin in PATH, mode 040777 ==> Downloading https://homebrew.bintray.com/bottles/node-7.10.0.sierra.bottle.tar Already downloaded: /Users/yuwen/Library/Caches/Homebrew/node-7.10.0.sierra.bottle.tar.gz ==> Pouring node-yuwentekiMacBook-Pro:~ yuwen$ brew
