Extending Quicklens (https://github.com/adamw/quicklens) to support sealed traits

SealedTest.scala

case class Grand(parent: Parent)
sealed trait Parent { def x: Int }
case class Child1(x: Int) extends Parent
case class Child2(x: Int) extends Parent

val grand = Grand(Child1(3))

it should "modify a field in a sealed trait" in {
  modify(grand)(_.parent.x).using(_ + 1) should be (Grand(Child1(4)))
}