COMP: Prefer the C++ headers over the C99 headers

Using the C++11 headers keeps the library cleaner and more
rigorously scoped use of namespaces.
diff --git a/src/jsontestrunner/main.cpp b/src/jsontestrunner/main.cpp
index 3b5e21a..28691a2 100644
--- a/src/jsontestrunner/main.cpp
+++ b/src/jsontestrunner/main.cpp
@@ -16,7 +16,7 @@
 #include <algorithm> // sort
 #include <json/json.h>
 #include <sstream>
-#include <stdio.h>
+#include <cstdio>
 
 struct Options {
   JSONCPP_STRING path;