Update readme.md (Azure#12452)

Author: Sandido

specification/compute/resource-manager/readme.md

@@ -219,8 +219,7 @@ input-file:
 - Microsoft.Compute/stable/2020-06-01/runCommands.json
 - Microsoft.Compute/stable/2019-04-01/skus.json
 - Microsoft.Compute/stable/2020-09-30/disk.json
-- Microsoft.Compute/preview/2020-09-30/gallery.json
-- Microsoft.Compute/preview/2020-09-30/sharedGallery.json
+- Microsoft.Compute/stable/2019-12-01/gallery.json
 - Microsoft.ContainerService/stable/2017-01-31/containerService.json
 - Microsoft.Compute/preview/2020-10-01-preview/cloudService.json
 ```