title: Add Boostrap 4 Alpha to Yii 2 advanced template with composer?
body: <p>How to add the Boostrap 4 alpha's into a <code>yii2-app-advanced</code> app, using <code>composer</code> and making it a dependancy?</p>
  
  <p>I've tried editing <code>vendor/yiisoft/yii2-bootstrap</code>, and adding <code>4.*</code> in it's <code>composer.json</code> on line <code>22</code>, but no avail:</p>
  
  <pre><code>"bower-asset/bootstrap": "3.3.* | 3.2.* | 3.1.* | 4.*"
  </code></pre>
  
  <p>It being an asset bundle or compatible with the current one (<code>v3</code>), is not that important to me. Just adding it properly and distributing it over my git repo.</p>
  
  <p>Thank you.</p>