title: Every chef commands gets error (Mac OS X)
body: <p>It looks like following:</p>
  
  <pre>
  $chef-client --version
  /opt/chef/embedded/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:774:in `block in activate_dependencies': can't satisfy 'mime-types (~> 1.16)', already activated 'mime-types-2.0' (Gem::LoadError)
      from /opt/chef/embedded/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:766:in `each'
      from /opt/chef/embedded/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:766:in `activate_dependencies'
      from /opt/chef/embedded/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:750:in `activate'
      from /opt/chef/embedded/lib/ruby/site_ruby/1.9.1/rubygems.rb:1232:in `gem'
      from /opt/chef/embedded/bin/chef-client:22:in `'
  </pre>
  
  <p>It is mean that I should reinstall ruby?or updated it? What kinds of  commands should be used?</p>