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
找到方法了：
https://github.com/thoughtbot/capybara-webkit/wiki/Installing-Qt-and-compiling-capybara-webkit
要这样装：
brew install qt