Update postgres

Changes:

- https://github.com/docker-library/postgres/commit/058c5c9: Update to 12~beta4-1.pgdg100+1
- https://github.com/docker-library/postgres/commit/5ad8e92: Update to 12beta4
- https://github.com/docker-library/postgres/commit/a74b452: Update generated README

library/postgres

@@ -4,14 +4,14 @@ Maintainers: Tianon Gravi <[email protected]> (@tianon),
              Joseph Ferguson <[email protected]> (@yosifkit)
 GitRepo: https://github.com/docker-library/postgres.git
 
-Tags: 12-beta3, 12
+Tags: 12-beta4, 12
 Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: 75ebadd71bd54836de126f851f5edbc2bdee4201
+GitCommit: 058c5c951f6870c538cb2039e93275bee242d373
 Directory: 12
 
-Tags: 12-beta3-alpine, 12-alpine
+Tags: 12-beta4-alpine, 12-alpine
 Architectures: amd64, arm32v6, arm32v7, arm64v8, i386, ppc64le, s390x
-GitCommit: d6e8fe3240b3d2c5d1a03f005360710812714163
+GitCommit: 5ad8e92a81fec890f33eb077e491ea82c76ac980
 Directory: 12/alpine
 
 Tags: 11.5, 11, latest