build: switch to C++17

Change-Id: Ie68020a04b7e20b74778b6d0370544ded55c5e26
diff --git a/tests/tools/nfdc/status-fixture.hpp b/tests/tools/nfdc/status-fixture.hpp
index 96edbba..f00b135 100644
--- a/tests/tools/nfdc/status-fixture.hpp
+++ b/tests/tools/nfdc/status-fixture.hpp
@@ -64,7 +64,7 @@
 class StatusFixture : public MockNfdMgmtFixture
 {
 protected:
-  using ValidatorUniquePtr = typename std::result_of<MakeValidator(Face&, KeyChain&)>::type;
+  using ValidatorUniquePtr = std::invoke_result_t<MakeValidator, Face&, KeyChain&>;
 
   StatusFixture()
     : validator(MakeValidator()(face, m_keyChain))