after some searching and trying to find an example, I found the answer.
The documentation of the featherlight.js is not that clear, but it is simply the answer. Just include the swipe_detec.js before including featherlight.js and it will enable touch swiping on mobile devices.
example
<html>
<head>
<!-- jquery -->
<script src="//code.jquery.com/jquery-latest.js"></script>
<!-- featherlight -->
<script src="//cdnjs.cloudflare.com/ajax/libs/detect_swipe/2.1.1/jquery.detect_swipe.min.js"></script>
<link href="//cdn.rawgit.com/noelboss/featherlight/1.3.4/release/featherlight.min.css" type="text/css" rel="stylesheet" />
<script src="//cdn.rawgit.com/noelboss/featherlight/1.3.4/release/featherlight.min.js" type="text/javascript" charset="utf-8"></script>
<!-- featherlight gallery -->
<link href="//cdn.rawgit.com/noelboss/featherlight/1.3.4/release/featherlight.gallery.min.css" type="text/css" rel="stylesheet" />
<script src="//cdn.rawgit.com/noelboss/featherlight/1.3.4/release/featherlight.gallery.min.js" type="text/javascript"></script>
</head>
<body>
<a class="thumbnail gallery" href="a.jpg" > <img src="a.jpg" /> </a>
<a class="thumbnail gallery" href="b.jpg" > <img src="b.jpg" /> </a>
<a class="thumbnail gallery" href="c.jpg" > <img src="c.jpg" /> </a>
<script>
$(document).ready(function(){
$('.gallery').featherlightGallery();
});
</script>
</body>
</html>
hope someone finds it useful.