title: Jpeg images in Xcode project reported to to be invalid
body: <p>After upgrading (Swift and Xcode - some time ago already), I now have a warning for every .JPG image in my project (I have 200+ JPG images in the project):</p>
  
  <blockquote>
    <p>The image set "Image1" references a file "Image1.JPG", but that file
    does not have a valid extension.</p>
  </blockquote>
  
  <p>How do I get rid of the warnings/fix the root cause of the issue?</p>