makefile: Fix rule ordering

Change-Id: I7f6cf155e5840693b519d366e39905595d838b9a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/Makefile.am b/src/Makefile.am
index 40bb24a..9148c7c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -20,7 +20,7 @@
 libgpioplus_la_SOURCES += gpioplus/internal/sys.cpp
 
 nobase_include_HEADERS += gpioplus/test/event.hpp
-nobase_include_HEADERS += gpioplus/test/sys.hpp
 nobase_include_HEADERS += gpioplus/test/handle.hpp
+nobase_include_HEADERS += gpioplus/test/sys.hpp
 
 nobase_include_HEADERS += gpioplus/utility/aspeed.hpp