Fix path to icon (#9276)

grafana_mask_icon.svg is located in the img/ folder.

public/views/index.html

@@ -17,7 +17,7 @@
 		[[end]]
 
     <link rel="icon" type="image/png" href="[[.AppSubUrl]]/public/img/fav32.png">
-    <link rel="mask-icon" href="[[.AppSubUrl]]/public/grafana_mask_icon.svg" color="#F05A28">
+    <link rel="mask-icon" href="[[.AppSubUrl]]/public/img/grafana_mask_icon.svg" color="#F05A28">
 		<base href="[[.AppSubUrl]]/" />
 
 	</head>