make laser double tap work on mobile browsers

public/trivabble.js

@@ -580,6 +580,11 @@
         return false;
     }
 
+    function touchStartTilePreventDefault(e) {
+        laserTouch(e);
+        return preventDefault(e);
+    }
+
     function makeLetter(letter, highlight, noEvents) {
         const tile = document.createElement("span");
         tile.translate = false;
@@ -593,7 +598,7 @@
             mouseDown(tile, dragTileBegin);
 
             tile.addEventListener("contextmenu", preventDefault);
-            tile.addEventListener("touchstart", preventDefault);
+            tile.addEventListener("touchstart", touchStartTilePreventDefault);
             tile.addEventListener("touchmove", preventDefault);
         }