title: PHP's json extension is required to use Monolog's NormalizerFormatter
body: <p>I'am new to symfony. I have created symfony project using:
  symfony new PhpSymfony // command.
  when i run project using:
  php bin/console server:run // command, app.php page is displayed in the browser (<a href="http://localhost:8000" rel="nofollow">http://localhost:8000</a>).
  But if I run without using the command php bin/console server:run,
  I will get an exception in the browser </p>
  
  <p>"RuntimeException in classes.php line 5493: PHP's json extension is required to use Monolog's NormalizerFormatter"</p>
  
  <p>I am running on <a href="http://localhost/app_dev.php" rel="nofollow">http://localhost/app_dev.php</a>
  and I a using apache2 server... 
  How to solve this problem ?</p>