mac 10.12.4
ruby 2.4
安装 nokogiri 失败。缺少libxml2 解决方法
gem install nokogiri -- --use-system-libraries=true --with-xml2-include=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/libxml2/