我跑了bundle install，我得到了这个错误:

Building nokogiri using system libraries.

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb --use-system-libraries
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.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
    --help
    --clean
    --use-system-libraries
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --with-xml2-dir
    --without-xml2-dir
    --with-xml2-include
    --without-xml2-include=${xml2-dir}/include
    --with-xml2-lib
    --without-xml2-lib=${xml2-dir}/lib
    --with-libxml-2.0-config
    --without-libxml-2.0-config
    --with-pkg-config
    --without-pkg-config
    --with-xslt-dir
    --without-xslt-dir
    --with-xslt-include
    --without-xslt-include=${xslt-dir}/include
    --with-xslt-lib
    --without-xslt-lib=${xslt-dir}/lib
    --with-libxslt-config
    --without-libxslt-config
    --with-pkg-config
    --without-pkg-config
    --with-exslt-dir
    --without-exslt-dir
    --with-exslt-include
    --without-exslt-include=${exslt-dir}/include
    --with-exslt-lib
    --without-exslt-lib=${exslt-dir}/lib
    --with-libexslt-config
    --without-libexslt-config
    --with-pkg-config
    --without-pkg-config

extconf failed, exit code 1

Gem files will remain installed in /Users/myuser/projectpath/vendor/bundle/ruby/2.0.0/gems/nokogiri-1.6.2.rc2 for inspection.
Results logged to /Users/myuser/projectpath/vendor/bundle/ruby/2.0.0/extensions/universal-darwin-13/2.0.0/nokogiri-1.6.2.rc2/gem_make.out
An error occurred while installing nokogiri (1.6.2.rc2), and Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.6.2.rc2'` succeeds before bundling.

你知道这是什么吗？

EDIT:

我还安装了instructions in the tutorial之后的nokogiri，奇怪的是gem安装成功了.当我运行gem list时，我有nokogiri (1.6.2.1)个，但当运行bundle install时，它会显示错误.