title: Error when bundle install-ing - `Bundler could not find compatible versions for gem "rails"`
body: <p>I'm trying to install a gem, I updated it in the gemfile, then <code>bundle install</code>.</p>
  
  <p>I received the following error message: </p>
  
  <pre><code>Bundler could not find compatible versions for gem "rails":
    In Gemfile:
      merchant_samples (&gt;= 0) ruby depends on
        rails (~&gt; 3.2.9) ruby
  
      rails (3.2.7)
  </code></pre>
  
  <p>What does it mean? What can I do? I'm using rvm, do I need to switch to another version of ruby? of rails? and if so, which one and how? and why :)</p>