Update the ftp manifest properties

CloudronManifest.json

@@ -14,9 +14,10 @@
   "addons": {
     "mysql": {},
     "localstorage": {
-        "ftp": {
-            "uid": "33/www-data"
-        }
+      "ftp": {
+        "uid": 33,
+        "uname": "www-data"
+      }
     },
     "sendmail": {},
     "ldap": {},