Replace the deprecated std::result_of with std::invoke_result

src/template.h

@@ -67,8 +67,7 @@ template <typename F, typename... T> struct Defer {
   Defer(Defer &&o) noexcept : f(std::move(o.f)) {}
   ~Defer() { f(); }
 
-  using ResultType = typename std::result_of<typename std::decay<F>::type(
-      typename std::decay<T>::type...)>::type;
+  using ResultType = std::invoke_result_t<F, T...>;
   std::function<ResultType()> f;
 };