Replace hexToRgb function to work with legacy mobile browsers

pyleds/templates/index.html

@@ -7,11 +7,12 @@
     <link rel="stylesheet" href="custom.css">
 
     <script type="text/javascript">
-        const hexToRgb = hex =>
-            hex.replace(/^#?([a-f\d])([a-f\d])([a-f\d])$/i
+        function hexToRgb(value) {
+            return value.replace(/^#?([a-f\d])([a-f\d])([a-f\d])$/i
                 ,(m, r, g, b) => '#' + r + r + g + g + b + b)
                 .substring(1).match(/.{2}/g)
                 .map(x => parseInt(x, 16));
+        }
 
         function show_loading(visible) {
             document.getElementById('loading').style.visibility = visible ? 'visible' : 'hidden';