Build: Fix iOS 12 by switching from iPhone 8 to iPhone XS

Cherry-picked from 26f13a7 (3.0.0-dev).

Author: Krinkle

build/browserstack-full.json

@@ -48,7 +48,7 @@
       "real_mobile": true
     },
     {
-      "device": "iPhone 8",
+      "device": "iPhone XS",
       "real_mobile": true,
       "os": "ios",
       "os_version": "12"