types: Fix typo in Silence.Matchers' documentation
types: Fix typo in Silence.Matchers' documentation

Signed-off-by: Kiril Vladimirov <453eedad0511e29ea8032567efcbc185237e0d60@vladimiroff.org>

GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager