List standard C headers in alphabetical order

Change-Id: I8a3f329ddafd61c0fbde88143e00931c6f1399e2

stats/rate_hist.c

diff --git a/stats/rate_hist.c b/stats/rate_hist.c
index 3287246..ff320bf 100644
--- a/stats/rate_hist.c
+++ b/stats/rate_hist.c
@@ -12,8 +12,8 @@
 #include "stats/rate_hist.h"
 
 #include <assert.h>
-#include <math.h>
 #include <limits.h>
+#include <math.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>