Ensure icon will work on GitHub page.

screenshots/index.html

@@ -19,7 +19,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Element X Android Gallery</title>
-    <link rel="icon" href="../.idea/icon.png">
+    <link rel="icon" href="https://raw.githubusercontent.com/element-hq/element-x-android/develop/.idea/icon.png">
     <link rel="stylesheet" href="html/screenshots.css">
 </head>
 <!-- load script which is in ./html/script.js -->