WebhookClient: Add missing @Override annotation

Change-Id: Ib12c066007bf51fe4c528ed33df5ff5f8d6d6518
diff --git a/src/main/java/com/cisco/gerrit/plugins/slack/client/WebhookClient.java b/src/main/java/com/cisco/gerrit/plugins/slack/client/WebhookClient.java
index af50032..81287b2 100644
--- a/src/main/java/com/cisco/gerrit/plugins/slack/client/WebhookClient.java
+++ b/src/main/java/com/cisco/gerrit/plugins/slack/client/WebhookClient.java
@@ -141,6 +141,7 @@
           Authenticator authenticator;
           authenticator =
               new Authenticator() {
+                @Override
                 public PasswordAuthentication getPasswordAuthentication() {
                   return (new PasswordAuthentication(
                       config.getProxyUsername(), config.getProxyPassword().toCharArray()));