message: Remove std::iterator
diff: @@ -210,10 +210,15 @@ class ExpandableTreeView {
  // node is visited unexpanded, or that node's children is visited; iteration
  // never visits both a node AND its children, only one or the other.
  template <class WrappedNodeType>
  -class ExpandableTreeView<WrappedNodeType>::iterator
  - : public std::iterator<std::forward_iterator_tag, const value_type> {
  +class ExpandableTreeView<WrappedNodeType>::iterator {
  friend class ExpandableTreeView<WrappedNodeType>; // grant access to private
  // constructor
  + public:
  + using iterator_category = std::forward_iterator_tag;
  + using value_type = typename TreeTraits::Value::type;
  + using difference_type = int;
  + using pointer = typename TreeTraits::Value::type*;
  + using reference = typename TreeTraits::Value::type&;
  private:
  explicit iterator(const impl_type* node) : node_(node) {}
  