build: Use AM_CPPFLAGS instead of INCLUDES
diff --git a/Makefile.am b/Makefile.am
index f802388..ee2c715 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -46,7 +46,7 @@
 					-DPLUGINDIR=\""$(plugindir)"\" \
 					-DPUSHCONFDIR=\""$(pushconfdir)"\"
 
-INCLUDES = -I$(builddir)/src -I$(srcdir)/src -I$(srcdir)/gdbus
+AM_CPPFLAGS = -I$(builddir)/src -I$(srcdir)/src -I$(srcdir)/gdbus
 
 CLEANFILES = src/builtin.h