Reorder includes. (#5749)

* Reorder includes.

* R.

src/common/hist_util.cc

@@ -2,19 +2,21 @@
  * Copyright 2017-2020 by Contributors
  * \file hist_util.cc
  */
+#include <numeric>
+#include <vector>
+
 #include <dmlc/timer.h>
 #include <dmlc/omp.h>
 
 #include <rabit/rabit.h>
-#include <numeric>
-#include <vector>
 
 #include "xgboost/base.h"
-#include "../common/common.h"
 #include "hist_util.h"
 #include "random.h"
 #include "column_matrix.h"
 #include "quantile.h"
+
+#include "../common/common.h"
 #include "./../tree/updater_quantile_hist.h"
 
 #if defined(XGBOOST_MM_PREFETCH_PRESENT)