change literal to config var

templates/progbar.html

     async function updateDistance() {
       var dist = await getDistance();
       var bar = document.getElementById("distance-bar");
-      var percentage = dist>2000 ? 100 : parseInt((100.0*dist)/MAX_DISTANCE);
+      var percentage = dist>MAX_DISTANCE ? 100 : parseInt((100.0*dist)/MAX_DISTANCE);
       bar.style.width=`${percentage}%`;
       bar.textContent = dist;
     }