Update CI jobs xcode/macOS version to match PyTorch core

xcode: 12.0
macOS: 10.15

See https://circleci.com/docs/2.0/testing-ios/#supported-xcode-versions

Author: mthrok

.circleci/config.yml

@@ -172,7 +172,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel
@@ -198,7 +198,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel

.circleci/config.yml.in

@@ -172,7 +172,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel
@@ -198,7 +198,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "9.4.1"
+      xcode: "12.0"
     steps:
       - checkout
       - designate_upload_channel