Typo in sample ml-config

[grtjn]

Sample user in ml-config has this roles definition:

  <role-names>
    <role-names>@ml.app-role</role-names>
  </role-names>

Just aesthetic, but that should be:

  <role-names>
    <role-name>@ml.app-role</role-name>
  </role-names>

(Inner element should be role-name without plural..)

Inner element-name seems to be ignored looking at the code, so both should work..