title: Laravel MIME Validator not working as expected
body: <p>i'm creating an API in Laravel 5.5 and this API supports receiving some files for profile pictures and such.</p>
  
  <p>I want to limit this through a <em>form request</em> to accept only <strong>JPG</strong> and <strong>PNG</strong> images and i'm setting up my Form Request as follows:</p>
  
  <pre><code>    'picture'    =&gt; 'nullable|image|mimetypes:image/jpeg,image/png,image/jpg|max:2000' // 2000KB or around 2MB per picture
  </code></pre>
  
  <p>Then, on my PHPUnit/Codeception tests i'm sending a fake image using Laravel's own <code>fake</code> static method as follows</p>
  
  <pre><code>'picture' =&gt; UploadedFile::fake()-&gt;image("hello.svg")
  </code></pre>
  
  <p>If i DD the image file that is being sent when i run the test it correctly lists it's <strong>MIMEType</strong> as <code>image/svg+xml</code>, however, somehow this passes validation and comes out the other end and that should not be the case as my rule <em>should</em> limit only PNG or JPG files.</p>
  
  <p>Does anyone else have this issue?</p>