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.