Use forked version of postgres 8 to avoid Docker image format version…

… issues.

See: https://docs.docker.com/engine/deprecated/#pushing-and-pulling-with-image-manifest-v2-schema-1

Forked images created by pulling the original image and pushing to the fork. For more details, see: golang-migrate#1143 (comment)

database/redshift/redshift_test.go

@@ -40,7 +40,7 @@ var (
 	}
 
 	specs = []dktesting.ContainerSpec{
-		{ImageName: "postgres:8", Options: opts},
+		{ImageName: "migrate/postgres8:8", Options: opts},
 	}
 )