update_engine: Sort 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 update_engine.

BUG=None
TEST=cpplint.py --filter=-build/include_order,+build/include_alpha update_engine/*
CQ-DEPEND=CL:209472

Change-Id: I261ea04681599a68ec7cb899f2f881cbe228ff7b
Reviewed-on: https://chromium-review.googlesource.com/209631
Reviewed-by: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/payload_state_interface.h b/payload_state_interface.h
index 5c648cb..36b8130 100644
--- a/payload_state_interface.h
+++ b/payload_state_interface.h
@@ -7,8 +7,8 @@
 
 #include <string>
 
-#include "update_engine/constants.h"
 #include "update_engine/action_processor.h"
+#include "update_engine/constants.h"
 #include "update_engine/omaha_response.h"
 
 namespace chromeos_update_engine {