Add Tifinagh to list of both-directions scripts
diff --git a/src/hb-common.cc b/src/hb-common.cc
index c9a4029..282a8e4 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -632,6 +632,7 @@
     case HB_SCRIPT_OLD_HUNGARIAN:
     case HB_SCRIPT_OLD_ITALIC:
     case HB_SCRIPT_RUNIC:
+    case HB_SCRIPT_TIFINAGH:
 
       return HB_DIRECTION_INVALID;
   }