title: Can't install JSON gem
body: <p>I need to install json because I get this error:</p>
  
  <p><code>Could not find json-1.4.6 in any of the sources</code></p>
  
  <p>I ran <code>gem install json</code> and <code>bundle install</code> but I was only able to install json-1.5.1 when I need json-1.4.6</p>
  
  <p>I have <code>gem 'json', '1.4.6'</code> in my gemfile, so I'm not sure what's going on...</p>
  
  <p>UPDATE</p>
  
  <p>I get this error: </p>
  
  <p>Installing json (1.4.6) /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/fileutils.rb:1216:in `chmod': Operation not permitted - /Library/Ruby/Gems/1.8/gems/json-1.4.6/CHANGES (Errno::EPERM)</p>