If you are getting following error:

PHP Notice:  date_default_timezone_set(): Timezone ID '' is invalid in /var/www/html/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/LoadConfiguration.php on line 45

[2017-10-16 19:50:38] production.ERROR: Symfony\Component\Debug\Exception\FatalThrowableError: Call to undefined method Illuminate\Foundation\Bootstrap\ConfigureLogging::configureHandler() 
                                                                                                 
  [Symfony\Component\Debug\Exception\FatalThrowableError]                                        
  Call to undefined method Illuminate\Foundation\Bootstrap\ConfigureLogging::configureHandler()  
                                                                                                 

Try editing composer.json and set laravel/framework to 5.*, e.g.

        "laravel/framework": "5.*",

Then run composer update again.
Also, make sure config/app.php exists!