FIX: Fix compilation with C++11

Author: threecgreen

include/databento/record.hpp

@@ -50,7 +50,7 @@ using void_t = void;
 template <typename, typename = detail::void_t<>>
 struct has_header : std::false_type {};
 template <typename T>
-struct has_header<T, std::void_t<decltype(std::declval<T>().hd)>>
+struct has_header<T, detail::void_t<decltype(std::declval<T>().hd)>>
     : std::is_same<decltype(std::declval<T>().hd), RecordHeader> {};
 template <typename T>
 constexpr bool has_header_v = has_header<T>::value;