我刚刚开始安装 SASS 和 COMPASS。下一步是安装 CSS_PARSER。这是一个非常简单的步骤，但是......我按照他们网站的说明插入了。将其插入终端：
sudo gem install css_parser
几秒钟后，它开始安装，但我收到此警报并且卡住了：
sudo gem install compass
Successfully installed compass-0.12.2
1 gem installed
Installing ri documentation for compass-0.12.2...
Installing RDoc documentation for compass-0.12.2...
Daniels-MacBook-Pro:~ DanielRamirez$ sudo gem install css_parser
Building native extensions. This could take a while...
ERROR: Error installing css_parser:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h
Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/json-1.7.7 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/json-1.7.7/ext/json/ext/generator/gem_make.out
这是什么意思，我该如何遵循？