Digraph warning

The original version can trigger a digraph-related warning in VS2015. Is this namespace construct a typo or something deliberate?

src/json.hpp

@@ -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