buffet: Sorted headers alphabetically (build/include_alpha)

We are going to enable build/include_alpha linter warning soon,
so in preparation for this, fixed the warnings in buffet.

BUG=None
TEST=cpplint.py --filter=-build/include_order,+build/include_alpha buffet/* buffet/commands/*

Change-Id: I103670d12f1eaec552d2ff21017316bb41b16b78
Reviewed-on: https://chromium-review.googlesource.com/209562
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/error_unittest.cc b/buffet/error_unittest.cc
index cf943ad..5db0012 100644
--- a/buffet/error_unittest.cc
+++ b/buffet/error_unittest.cc
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <gtest/gtest.h>
 #include <base/files/file_path.h>
+#include <gtest/gtest.h>
 
 #include "buffet/error.h"