fix attribute translation for activerecord using STI having with both singular(one) and plural(other) translation keys

fix translated_ancestor_attributes for Active Record attributes translated like this

activerecord:
  attributes:
    family:
      child:
        one: child
        other: children

by preceding the key `family.child` with `family.child.one` in the returned array. 
If `family.child.one` is missing (meaning that no separate translation for singular/plural exists) it will be ignored and `family.child` will be used.