upgrade prometheus client-go

Signed-off-by: zackzhangkai <zackzhang@yunify.com>

vendor/github.com/prometheus/alertmanager/COPYRIGHT.txt

@@ -0,0 +1,12 @@
+Copyright Prometheus Team
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.