title: mysqli not found when running on server
body: <p>When I run my app on local host, I don't have any trouble, but when it is running on heroku I get this error:
  Fatal error: Class 'mysqli' not found in /app/www/db.php on line 13</p>
  
  <p>I ran this code to check it: </p>
  
  <pre><code>if (!function_exists('mysqli_init') &amp;&amp; !extension_loaded('mysqli')) {
  
      echo 'We don\'t have mysqli!!!';
  
  } else {
  
      echo 'Phew we have it!';
  
  }
  </code></pre>
  
  <p>When I run this on localhost I get "Phew we have it!" but when I run it on heroku I get "We don't have mysqli!!!".
  I have no idea what the problem is, so any help would be great.</p>