title: Laravel voyager validation
body: <p>I try to use validation in Laravel Voyager. When I set validation rule for image like</p>
  
  <pre><code>    {
      "validation": {
          "rule": 
    "required|image|mimes:jpeg,png,jpg,gif,svg|max:2048|dimensions:width=500,height=500"
      }
  }
  </code></pre>
  
  <p>Though I have select an image it always shows an error <code>The default img field is required.</code> </p>
  
  <p>But If I remove the <code>required</code> part from the validation rule like </p>
  
  <pre><code>    {
      "validation": {
          "rule": "image|mimes:jpeg,png,jpg,gif,svg|max:2048|dimensions:width=500,height=500"
      }
  }
  </code></pre>
  
  <p>Then it doesn't show any error though I have select an image with below dimension.</p>
  
  <p>Is there any error ?</p>