feat(webkit): bump to 1321 (microsoft#3270)

The Windows browser archive is now 38Mb compared to 51Mb in 1320.

Author: yury-s

browsers.json

@@ -13,7 +13,7 @@
     },
     {
       "name": "webkit",
-      "revision": "1320",
+      "revision": "1321",
       "download": true
     }
   ]