安装ruby的gem -> capybara-webkit时，

gem install capybara-webkit -v '0.14.2'

出现如下错误：

Building native extensions.  This could take a while...
ERROR:  Error installing capybara-webkit:
    ERROR: Failed to build gem native extension.

    /Users/username/.rbenv/versions/2.0.0-p0/bin/ruby extconf.rb
Command 'qmake -spec macx-g++' not available


Gem files will remain installed in /Users/username/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/capybara-webkit-0.14.2 for inspection.
Results logged to /Users/username/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/capybara-webkit-0.14.2/./gem_make.out

Qt的安装方法是在官网下载Mac版并安装：

http://qt-project.org/downloads