title: flex-grow-1 not working in some versions of bootstrap
body: <p><code>flex-grow-1</code> is working with if use bootstrap 4.1.3 copied from <a href="https://www.w3schools.com/bootstrap4/tryit.asp?filename=trybs_flex-grow&amp;stacked=h" rel="nofollow noreferrer">w3school sample</a></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;head&gt;
    &lt;!-- flex-grow-1 is working with these libraries --&gt;
    &lt;!-------------------------------------------------&gt;
    &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css"&gt;
    &lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"&gt;&lt;/script&gt;
    &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"&gt;&lt;/script&gt;
    &lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div class="container mt-3"&gt;
      &lt;div class="d-flex mb-3"&gt;
        &lt;div class="p-2 bg-info"&gt;Flex item 1&lt;/div&gt;
        &lt;div class="p-2 flex-grow-1 bg-primary"&gt;Flex item 2&lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/body&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>But if I used bootstrap 4.0.0 CDNs that are provided in <a href="https://getbootstrap.com/docs/4.0/getting-started/introduction/" rel="nofollow noreferrer">Bootstrap 4 official page</a>, then <code>flex-grow-1</code> class does not work - seems that the class not exists:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;head&gt;
    &lt;!-- flex-grow-1 is not working with these libraries --&gt;
    &lt;!-----------------------------------------------------&gt;
    &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous"&gt;
    &lt;script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"&gt;&lt;/script&gt;
    &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"&gt;&lt;/script&gt;
    &lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div class="container mt-3"&gt;
      &lt;div class="d-flex mb-3"&gt;
        &lt;div class="p-2 bg-info"&gt;Flex item 1&lt;/div&gt;
        &lt;div class="p-2 flex-grow-1 bg-primary"&gt;Flex item 2&lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/body&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <hr>
  
  <h2>Questions:</h2>
  
  <ol>
  <li><p>Is this a bug? Or am I making a mistake? </p></li>
  <li><p>The reason I am reluctant to use Bootstrap version 4.1.3 CDN is that they don't have the <code>integrity</code> and <code>crossorigin</code> security fields. Is there any CDN for version 4.1.3 which does have these security fields?</p></li>
  </ol>