Fix web app manifest (#3582)

webapp/root.html

@@ -29,7 +29,7 @@
     <link rel='icon' type='image/png' sizes='32x32' href='images/favicon/favicon-32x32.png'>
     <link rel='icon' type='image/png' sizes='96x96' href='images/favicon/favicon-96x96.png'>
     <link rel='icon' type='image/png' sizes='192x192' href='images/favicon/android-chrome-192x192.png'>
-    <link rel='manifest' href='/static/config/manifest.json'>
+    <link rel='manifest' href='config/manifest.json'>
     <!-- Android add to homescreen -->
 
     <!-- CSS Should always go first -->