Update the iterator implementation for C++17 (jbeder#575)

Fix the compiler error which prevents deriving from std::iterator in C++17

include/yaml-cpp/node/detail/iterator.h

@@ -8,19 +8,19 @@
 #endif
 
 #include "yaml-cpp/dll.h"
+#include "yaml-cpp/node/detail/node_iterator.h"
 #include "yaml-cpp/node/node.h"
 #include "yaml-cpp/node/ptr.h"
-#include "yaml-cpp/node/detail/node_iterator.h"
 #include <cstddef>
 #include <iterator>
 
+
 namespace YAML {
 namespace detail {
 struct iterator_value;
 
 template <typename V>
-class iterator_base : public std::iterator<std::forward_iterator_tag, V,
-                                           std::ptrdiff_t, V*, V> {
+class iterator_base {
 
  private:
   template <typename>
@@ -37,7 +37,11 @@ class iterator_base : public std::iterator<std::forward_iterator_tag, V,
   };
 
  public:
-  typedef typename iterator_base::value_type value_type;
+  using iterator_category = std::forward_iterator_tag;
+  using value_type = V;
+  using difference_type = std::ptrdiff_t;
+  using pointer = V*;
+  using reference = V;
 
  public:
   iterator_base() : m_iterator(), m_pMemory() {}
@@ -86,7 +90,7 @@ class iterator_base : public std::iterator<std::forward_iterator_tag, V,
   base_type m_iterator;
   shared_memory_holder m_pMemory;
 };
-}
-}
+}  // namespace detail
+}  // namespace YAML
 
 #endif  // VALUE_DETAIL_ITERATOR_H_62B23520_7C8E_11DE_8A39_0800200C9A66