Update CI jobs xcode/macOS version to match PyTorch core (#1300)

Author: mthrok

.circleci/config.yml

@@ -174,7 +174,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel
@@ -200,7 +200,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel

.circleci/config.yml.in

@@ -174,7 +174,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel
@@ -200,7 +200,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel