Dockerfile: Using the recommended label syntax for maintainer (#1533)
Dockerfile: Using the recommended label syntax for maintainer (#1533)

Signed-off-by: Tariq Ibrahim <015a714bac3241e52706046ad89e44af1b63d7b3@microsoft.com>
GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager,prometheus/alertmanager