Small fix for favicon

src/index.html

@@ -9,7 +9,7 @@
 
     <title>Grafana</title>
     <link rel="stylesheet" href="css/grafana.dark.min.css" title="Dark">
-    <link rel="icon" type="image/png" href="img/fav_dark_16.png">
+    <link rel="icon" type="image/png" href="img/fav32.png">
 
     <!-- build:js app/app.js -->
     <script src="vendor/require/require.js"></script>