title: Symfony demo app install fails - pdo_sqlite missing
body: <p>I am trying to use the Symfony 4 demo application <a href="https://github.com/symfony/demo" rel="noreferrer">https://github.com/symfony/demo</a> but when I install it with composer I get the error described below.  I am using Ubuntu 16.04 and php 7.1 installed via phpbrew.</p>
  
  <p>My steps are as follows:</p>
  
  <pre><code>$ cd /var/www/html
  $ phpbrew use php-7.1.13
  $ sudo php composer.phar create-project symfony/symfony-demo
  </code></pre>
  
  <p>which yields this error:</p>
  
  <pre><code>Your requirements could not be resolved to an installable set of packages.
  
    Problem 1
  - The requested PHP extension ext-pdo_sqlite * is missing from your system. Install or enable PHP's pdo_sqlite extension.
  </code></pre>
  
  <p>if I check which extensions are loaded:</p>
  
  <pre><code>$ phpbrew extension
  </code></pre>
  
  <p>I get </p>
  
  <pre><code>Loaded extensions:
  ...
  [*] pdo_sqlite
  </code></pre>
  
  <p>so it appears that extension is loaded.</p>
  
  <p>What am I doing wrong please?</p>