Update CircleCI Xcode image (#1818) (#1870)

CircleCI is removing Xcode 12.4.0 image on August, and there was a planned
burnout on July 6th.

https://app.circleci.com/pipelines/github/pytorch/text/5996/workflows/0bfa021d-b532-4385-b406-c56373c8e9ce/jobs/204435

This commit updates Xcode image to 12.5

Co-authored-by: moto <[email protected]>

Author: atalman

.circleci/config.yml

@@ -203,7 +203,7 @@ jobs:
   binary_macos_wheel:
     <<: *binary_common
     macos:
-      xcode: "12.0"
+      xcode: "12.5"
     steps:
       - checkout
       - designate_upload_channel
@@ -229,7 +229,7 @@ jobs:
   binary_macos_conda:
     <<: *binary_common
     macos:
-      xcode: "12.0"
+      xcode: "12.5"
     steps:
       - checkout
       - designate_upload_channel
@@ -437,7 +437,7 @@ jobs:
   unittest_macos:
     <<: *binary_common
     macos:
-      xcode: "12.0"
+      xcode: "12.5"
     resource_class: large
     steps:
       - checkout