Use new form of type traits available in C++14

Author: joto

include/protozero/basic_pbf_builder.hpp

@@ -40,7 +40,7 @@ namespace protozero {
 template <typename TBuffer, typename T>
 class basic_pbf_builder : public basic_pbf_writer<TBuffer> {
 
-    static_assert(std::is_same<pbf_tag_type, typename std::underlying_type<T>::type>::value,
+    static_assert(std::is_same<pbf_tag_type, std::underlying_type_t<T>>::value,
                   "T must be enum with underlying type protozero::pbf_tag_type");
 
 public:

include/protozero/pbf_message.hpp

@@ -64,7 +64,7 @@ namespace protozero {
 template <typename T>
 class pbf_message : public pbf_reader {
 
-    static_assert(std::is_same<pbf_tag_type, typename std::underlying_type<T>::type>::value,
+    static_assert(std::is_same<pbf_tag_type, std::underlying_type_t<T>>::value,
                   "T must be enum with underlying type protozero::pbf_tag_type");
 
 public: