title: "gem install rails" give FilePermissionError with rbenv on mac OS X
body: <p>I've read all the other Stackoverflow posts on this problem but don't see any suitable solution for rbenv, so i'll post it on here. (most of the other posts suggest either using RVM, or the OP had already ran <code>sudo gem install rails</code>).</p>
  
  <p>when i run <code>gem install rails</code>  (without <code>sudo</code>), i get</p>
  
  <pre><code>ERROR:  While executing gem ... (Gem::FilePermissionError)
      You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
  </code></pre>
  
  <ol>
  <li><p>is <code>/Library/Ruby/Gems/2.0.0</code> the correct spot?</p></li>
  <li><p>why am i getting this error? i'm on a fresh laptop that hasn't had much install. </p></li>
  </ol>
  
  <p>i've got homebrew, rbenv, and ruby 2.0</p>