Copied parMap from answers section

Otherwise the solution for parFoldMap in Monoid.scala won't compile

  def parFoldMap[A,B](v: IndexedSeq[A], m: Monoid[B])(f: A => B): Par[B] =
    Par.parMap(v)(f).flatMap { bs =>
      foldMapV(bs, par(m))(b => Par.lazyUnit(b))
    }