title: Laravel 5.7.17 file validation issue
body: <p>The example is based on Laravel's registration. </p>
  
  <p>I have added following to register.blade.php:</p>
  
  
  
  <pre class="lang-php prettyprint-override"><code>&lt;div class="form-group row"&gt;
      &lt;label for="file" class="col-md-4 col-form-label text-md-right"&gt;{{ __('Files') }}&lt;/label&gt;
  
      &lt;div class="col-md-6"&gt;
          &lt;input type="file" id="files" name="files[]" multiple&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The method in RegisterController looks like this:</p>
  
  <pre class="lang-php prettyprint-override"><code>protected function validator(array $data)
  {
      $validator = Validator::make($data, [
          'name' =&gt; ['required', 'string', 'max:255'],
          'files.*' =&gt; ['required', 'file'],
      ]);
  
      dd($validator-&gt;errors());
  }
  </code></pre>
  
  <p>I'm trying to upload a PDF and a DOC file.:</p>
  
  <pre class="lang-php prettyprint-override"><code>MessageBag {#236 ▼
    #messages: array:2 [▼
      "files.0" =&gt; array:1 [▼
        0 =&gt; "The files.0 must be a file."
      ]
      "files.1" =&gt; array:1 [▼
        0 =&gt; "The files.1 must be a file."
      ]
    ]
    #format: ":message"
  }
  </code></pre>
  
  <p>Must be a file? These are files...</p>