ci: fix deprecated macOS config

Author: cwillisf

.circleci/config.yml

@@ -29,9 +29,10 @@ aliases:
 jobs:
   build_for_macos:
     macos:
-      # CircleCI's Xcode 12.4.0 image is the last of their images to be based on macOS 10.15
-      # CircleCI no longer supports Xcode 11+ on macOS 10.14
-      xcode: 12.4.0
+      # CircleCI's Xcode 11.7.0 image is the last of their images to be based on macOS 10.15
+      # CircleCI no longer supports macOS 10.14, and Xcode 12 on macOS 10.15 has been removed as well
+      xcode: 11.7.0
+    resource_class: macos.x86.medium.gen2 # "medium" has been deprecated
     steps:
       - checkout
       - npm_install:
@@ -58,6 +59,8 @@ jobs:
           key: homebrew-cache-v2
       - run:
           name: Work around electron-userland/electron-builder#4964
+          environment:
+            HOMEBREW_NO_AUTO_UPDATE: 1
           command: |
             brew install go go-bindata
             git -C ~ clone https://github.com/develar/app-builder.git