Suppress pgn4web files from being converted by 'jekyll-assets'.

_layouts/game.html

@@ -24,7 +24,7 @@ layout: default
 </div>
 
 <!-- pgn4web JavaScript -->
-{% javascript pgn4web %}
+<script src="/assets/js/pgn4web.js"></script>
 
 <script type="text/javascript">
  "use strict";