title: How to set custom error message on array input validation?
body: <p>in my form there is dynamic selects and I validate them via Laravel 5 usin <code>Request</code> class:</p>
  
  <pre><code>$rules = [
     'address' =&gt; 'sometimes|required|max:70',
     'area' =&gt; 'sometimes|required|numeric|max:10000',
  ];
  foreach ($this-&gt;request-&gt;get('category') as $key =&gt; $val) {
      $rules['category.' . $key] = 'sometimes|required|exists:categories,id';
  }
  </code></pre>
  
  <p>But validation errors I can't change and displays something like this:</p>
  
  <p><code>Field category.0 is required</code>, I tried to change <code>custom</code> array in <code>validation.php</code> file like this:</p>
  
  <pre><code>'custom' =&gt; [
      'category.0' =&gt; [
          'required' =&gt; 'Category is required field'
      ],
  </code></pre>
  
  <p>But it didn't change anything.</p>