[graphite2] Fix include

src/hb-graphite2.h

diff --git a/src/hb-graphite2.h b/src/hb-graphite2.h
index bea68f9..3eae54a 100644
--- a/src/hb-graphite2.h
+++ b/src/hb-graphite2.h
@@ -28,6 +28,8 @@
 
 #include "hb.h"
 
+#include <graphite2/Font.h>
+
 HB_BEGIN_DECLS