title: Can't install sprockets-es6 gem because of sprockets dependecy
body: <p>I'm new to Rails, and am trying to change an existing Rails app to use ES6 over Coffeescript. I've looked <a href="http://blog.arkency.com/2015/05/start-using-es6-with-rails-today/" rel="nofollow">around</a> <a href="http://blog.kwanso.com/using-ecmascript-6-with-rails-4-2-projects/" rel="nofollow">online</a> and seems like it should be as simple as adding the following to my Gemfile to get started with transpiling Babel:</p>
  
  <pre><code>gem 'sprockets'
  gem 'sprockets-es6', require: 'sprockets/es6'
  </code></pre>
  
  <p>When I add this and then <code>bundle install</code> I get the following error:</p>
  
  <pre><code>Bundler could not find compatible versions for gem "sprockets":
    In Gemfile:
      rails (= 3.2.21) ruby depends on
        railties (= 3.2.21) ruby depends on
          actionpack (= 3.2.21) ruby depends on
            sprockets (~&gt; 2.2.1) ruby
  
      sprockets (&gt;= 3.0.0.beta) ruby
  </code></pre>
  
  <p>I'm <em>really</em> not all that familiar with Rails, but my understanding is that specified Rails gem is incompatible with the specified Sprockets gem, right? Can someone point me in the right direction about how I can resolve this?</p>