Change Windows image back to stable (facebook#8424)

Summary:
Since windows timeout issue has been fixed. Change the image back to
stable.

Pull Request resolved: facebook#8424

Test Plan: Check CircleCI jobs

Reviewed By: zhichao-cao

Differential Revision: D29235219

Pulled By: akankshamahajan15

fbshipit-source-id: 2c111f96e216dac4ae3d7ec3b4cdd8e459575d37

.circleci/config.yml

@@ -124,7 +124,7 @@ commands:
 executors:
   windows-2xlarge:
     machine:
-      image: 'windows-server-2019-vs2019:previous'
+      image: 'windows-server-2019-vs2019:stable'
       resource_class: windows.2xlarge
       shell: bash.exe