我正在尝试在我的Mac（Yosemite）上安装Rails。我已经经历了几个SO问题，用Homebrew重新安装libxml2，用RVM重新安装，以及更新Ruby等等，到目前为止还没有任何工作。我的libxml2版本是2.9.2。
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
Building nokogiri using system libraries.
libxml2 version 2.6.21 or later is required!
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
我接下来应该尝试什么？