Add aria label to preview button

Author: chriskthomas

src/index.php

@@ -179,7 +179,7 @@
     </div>
   </footer>
 
-  <button id="previewButton">
+  <button id="previewButton" aria-label="Preview">
     <ion-icon name="eye"></ion-icon>
   </button>
   <div id="previewBlock"></div>
@@ -189,4 +189,4 @@
   <script nomodule src="<?= $ionicons_source ?>/dist/ionicons/ionicons.js"></script>
 </body>
 
-</html>
+</html>