Replace use of deprecated C Standard library headers in C++ code.

Change-Id: I9fa6630c7e4bdb2897df34d417635d8c7d8253bc
Signed-off-by: Tyler Chatow <tchatow@gmail.com>
diff --git a/aos/testing/random_seed.cc b/aos/testing/random_seed.cc
index 9e7136f..8f26d07 100644
--- a/aos/testing/random_seed.cc
+++ b/aos/testing/random_seed.cc
@@ -1,6 +1,6 @@
 #include "aos/testing/random_seed.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 
 namespace aos {
 namespace testing {