aapt: expat exports its header files now.

Change-Id: Iddf0133919d38fc896f97c6796f8228a6decf174
diff --git a/tools/aapt2/SourceXmlPullParser.h b/tools/aapt2/SourceXmlPullParser.h
index 15936d6..d8ed459 100644
--- a/tools/aapt2/SourceXmlPullParser.h
+++ b/tools/aapt2/SourceXmlPullParser.h
@@ -20,7 +20,7 @@
 #include "XmlPullParser.h"
 
 #include <istream>
-#include <libexpat/expat.h>
+#include <expat.h>
 #include <queue>
 #include <stack>
 #include <string>