[arabic] Update to latest UTR#53

From Lorna Evans: "That was a new character added to Unicode 11.0"

src/hb-ot-shape-complex-arabic.cc

@@ -611,6 +611,7 @@ modifier_combining_marks[] =
   0x06E3u, /* ARABIC SMALL LOW SEEN */
   0x06E7u, /* ARABIC SMALL HIGH YEH */
   0x06E8u, /* ARABIC SMALL HIGH NOON */
+  0x08D3u, /* ARABIC SMALL LOW WAW */
   0x08F3u, /* ARABIC SMALL HIGH WAW */
 };