From 1ab33ec5fbf88768cb1ef22cb8a5873cb757d4fc Mon Sep 17 00:00:00 2001
From: Dan Field <dfield@gmail.com>
Date: Fri, 2 Nov 2018 20:02:07 -0700
Subject: [PATCH] Update `osx_instance` (#23883)

* Update `osx_instance`

Cirrus no longer supports `high-sierra-xcode-9.4`.