Replace usage of std::result_of with std::invoke_result

C++17 deprecates `std::result_of` in favour of `std::invoke_result`.
Updating our code to use the replacement avoids the use of the
reprecated version.

Author: thomasspriggs

src/util/range.h

@@ -420,7 +420,7 @@ struct ranget final
   template <typename functiont>
   auto map(functiont &&f)
   {
-    using outputt = typename std::result_of<functiont(value_type)>::type;
+    using outputt = typename std::invoke_result<functiont, value_type>::type;
     auto shared_f = std::make_shared<
       std::function<outputt(const typename iteratort::value_type &)>>(
       std::forward<functiont>(f));