title: I can't register components using React_on_Rails gem
body: <p>The registration was working fine with the default HelloWorld app, but once I deleted the folder and created my own, it stopped working.</p>
  
  <p>I made a new folder under app/bundles called posts with a startup folder.</p>
  
  <p>In the startup folder, I'm registering the components like so:</p>
  
  <pre><code>import ReactOnRails from 'react-on-rails';
  
  import PostContainer from '../containers/PostContainer';
  
  ReactOnRails.register({
    PostContainer
  });
  </code></pre>
  
  <p>The PostContainer.jsx file is in the containers folder and it looks like this:</p>
  
  <pre><code>import React, { PropTypes, Component } from 'react';
  
  export default class PostsContainer extends React.Component {
    render() {
      return (
        &lt;div&gt;
          &lt;Header /&gt;
          &lt;PostList posts={this.props.posts} /&gt;
        &lt;/div&gt;
      )
    }
  }
  </code></pre>
  
  <p>My webpack.config.js file looks like this:</p>
  
  <pre><code>entry: [
      'es5-shim/es5-shim',
      'es5-shim/es5-sham',
      'babel-polyfill',
      './app/bundles/HelloWorld/startup/registration',
    ],
  </code></pre>
  
  <p>I tried changing the HelloWorld to posts or Posts, but it did not work.</p>
  
  <p>Am I supposed to have a file called webpack.configure.build.js? Or is the webpack.config.js the file I need to edit?</p>
  
  <p>Any help would be appreciated!</p>