title: Update ruby version on MAC
body: <p>I'm trying to update ma ruby version.
  I'm with ruby 1.8.7 and I would like to install 2.1.0.
  I just installed <code>rvm</code>, <code>rbenv</code>, <code>brew</code> and gem.</p>
  
  <p>But when I try to do </p>
  
  <pre><code>$ rbenv install 2.1.0.
  </code></pre>
  
  <p>I get an error about clang. I don't get the point between clang and ruby</p>
  
  <p>Could you please help me?</p>
  
  <p>Error:</p>
  
  <pre><code>$ rbenv install 2.1.0
  Downloading ruby-2.1.0.tar.gz...
  Installing ruby-2.1.0...
  
  BUILD FAILED
  ...
  Last 10 log lines:
  ...
  checking build system type... x86_64-apple-darwin12.3.0
  checking host system type... x86_64-apple-darwin12.3.0
  checking target system type... x86_64-apple-darwin12.3.0
  checking for gcc-4.2... no
  checking for clang... no
  checking for gcc... no
  checking for cc... no
  ./configure: line 3390: -E: command not found
  configure: error: clang version 3.0 or later is required
  </code></pre>