src: fix build/c++tr1 cpplint warnings

PR-URL: https://github.com/nodejs/node/pull/7462
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

src/util.h

@@ -8,6 +8,12 @@
 #include <stddef.h>
 #include <stdlib.h>
 
+#ifdef __APPLE__
+#include <tr1/type_traits>  // NOLINT(build/c++tr1)
+#else
+#include <type_traits>  // std::remove_reference
+#endif
+
 namespace node {
 
 #define FIXED_ONE_BYTE_STRING(isolate, string)                                \