Reports non-standard methods to extract keys from Map.

Example:


  val map = Map(1 -> 42)
  map.map(_._1)
  map.map(_._1).toSet
  map.map(_._1).toIterator

After the quick-fix is applied:


  val map = Map(1 -> 42)
  map.keys
  map.keySet
  map.keysIterator