Add Unicode 8.0 scripts

Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1183209
diff --git a/src/hb-common.cc b/src/hb-common.cc
index 21d3b41..d510c9b 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -493,6 +493,9 @@
     case HB_SCRIPT_PALMYRENE:
     case HB_SCRIPT_PSALTER_PAHLAVI:
 
+    /* Unicode-8.0 additions */
+    case HB_SCRIPT_OLD_HUNGARIAN:
+
       return HB_DIRECTION_RTL;
   }