message: Digraph warning
  The original version can trigger a digraph-related warning in VS2015. Is this namespace construct a typo or something deliberate?
diff: @@ -14492,7 +14492,7 @@ struct hash<nlohmann::json>
  /// specialization for std::less<value_t>
  template<>
  -struct less<::nlohmann::detail::value_t>
  +struct less<nlohmann::detail::value_t>
  {
  /*!
  @brief compare two value_t enum values
  