title: Laravel Livewire - Constant expression contains invalid operations in $rules property
body: <p>I tried to define some validation rules in my <code>livewire</code> component to validate some FormData:</p>
  <pre><code>protected $rules = [
      'website' =&gt; 'url|nullable',
      'zipcode' =&gt; 'regex:/\b\d{5}\b/|nullable',
      'founding_year' =&gt; 'required|digits:4|integer|min:1700|max:2020',
  ];
  </code></pre>
  <p>That work's very well until I need to validate against the value of a variable or a dynamic value in general.</p>
  <p>E.g.: Changing the <code>max</code> property from hardcoded <strong>2020</strong> to the <strong>current year</strong>:</p>
  <pre><code> protected $rules = [
     ...
     'founding_year' =&gt; 'required|digits:4|integer|min:1700|max:'. date('Y'),
  ];
  </code></pre>
  <p>Unfortunatelly this resolves in an exception:</p>
  <blockquote>
  <p>Symfony\Component\ErrorHandler\Error\FatalError</p>
  <p>Constant expression contains invalid operations</p>
  </blockquote>
  <p>Has someone an idea how to fix this?</p>