diff --git a/index.html b/index.html
index 70774d1..0dee12c 100644
--- a/index.html
+++ b/index.html
@@ -469,6 +469,8 @@ <h1>Play Quoridor against AI</h1>
         "use strict";
         // For some touch device, @media (hover: hover) is activated
         // (it is intended not to be activated), so add this workaround.
+        // Code below is based on:
+        // https://codeburst.io/the-only-way-to-detect-touch-with-javascript-7791a3346685
         window.addEventListener('touchstart', function onFirstTouch() {
             controller.view.isHoverPossible = false;
             controller.view.button.confirm.style.display = "inline-block";
diff --git a/sw.js b/sw.js
index 916ec94..3e65811 100644
--- a/sw.js
+++ b/sw.js
@@ -9,7 +9,7 @@
 * https://developers.google.com/web/fundamentals/primers/service-workers/
 */
 
-const CACHE_NAME = 'quoridor-ai-cache-v0.3.19';
+const CACHE_NAME = 'quoridor-ai-cache-v0.3.20';
 const urlsToCache = [
     './',
     './style.css',