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

fix translated_ancestor_attributes for activerecord attributes translated like this

activerecord:
  attributes:
    familiy:
      child:
        one: child
        other: children

by preceeding 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.