title: php 7.1.14 does not work with laravel 5.6
body: <p>I just got started with laravel 5.6 got php 7.2.4 and latest version of laravel 5.6 which is according to docs requires PHP >= 7.1.3 , but the laravel fails , when I run <code>phpunit</code> and it thorws this error:</p>
  
  <pre><code>Parse error: syntax error, unexpected ':' 
  in C:\laragon\www\forum\vendor\laravel\framework\src\Illuminate\Foundation\helpers.php 
  on line 233
  </code></pre>
  
  <p>and this is the line with the error: </p>
  
  <pre><code>return app('cache')-&gt;get($arguments[0], $arguments[1] ?? null);
  </code></pre>
  
  <p>and the problem is that php 7 does not support <code>??</code> operator so what is going on ? what version of php should I use with laravel 5.6 ?
  if I fix that line I have an error on another line , should I fix all this errors by myself ? please help</p>